結果

問題 No.1551 誕生日の三角形
ユーザー re_re0101re_re0101
提出日時 2021-06-18 21:22:17
言語 C++14
(gcc 12.3.0 + boost 1.83.0)
結果
AC  
実行時間 2 ms / 1,000 ms
コード長 29,731 bytes
コンパイル時間 1,995 ms
コンパイル使用メモリ 198,964 KB
実行使用メモリ 6,948 KB
最終ジャッジ日時 2024-06-22 19:47:19
合計ジャッジ時間 2,447 ms
ジャッジサーバーID
(参考情報)
judge4 / judge2
このコードへのチャレンジ
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テストケース

テストケース表示
入力 結果 実行時間
実行使用メモリ
testcase_00 AC 2 ms
6,812 KB
testcase_01 AC 2 ms
6,944 KB
testcase_02 AC 1 ms
6,940 KB
testcase_03 AC 2 ms
6,940 KB
testcase_04 AC 1 ms
6,948 KB
testcase_05 AC 1 ms
6,940 KB
testcase_06 AC 2 ms
6,944 KB
testcase_07 AC 2 ms
6,940 KB
testcase_08 AC 2 ms
6,944 KB
testcase_09 AC 2 ms
6,944 KB
testcase_10 AC 2 ms
6,940 KB
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ソースコード

diff #

// #pragma GCC optimize ("O3")
// #pragma GCC target("avx512f")
// #pragma GCC optimize("unroll-loops")
// #ifndef ONLINE_JUDGE
// #define _GLIBCXX_DEBUG
// #endif
#include<bits/stdc++.h>
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// #include <boost/rational.hpp>
// namespace mp = boost::multiprecision;
// using Bint=mp::cpp_int;
// using Real = mp::number<mp::cpp_dec_float<1024>>;
// #include<atcoder/all>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define bit(n,k) (((ll)n>>(ll)k)&1) /*nのk bit目*/
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define eb emplace_back
#define endl '\n'
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define PI 3.14159265359
const double eps = 1e-12;
const long long INF= (long long)1e18+20;
const int inf= 1010101010;
typedef long double D;      // 座標値の型。doubleかlong doubleを想定
typedef complex<D> Point;  // Point
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl>vvl;
typedef vector<vvl>vvvl;
typedef vector<vvvl>vvvvl;
typedef vector<vvvvl>vvvvvl;
typedef vector<int>vi;
typedef vector<vi>vvi;
typedef vector<vvi>vvvi;
typedef vector<vvvi>vvvvi;
typedef vector<vvvvi>vvvvvi;
typedef pair<ll,ll> P;
// typedef double D;    
template<class T> using minpq=priority_queue<T,vector<T>,greater<T>>;
const ll MOD=1000000007LL;
// const ll MOD=998244353LL;
const ll mod=MOD;
vl dx={0,0,1,-1,1,1,-1,-1};
vl dy={1,-1,0,0,-1,1,-1,1};


template<class T> vector<T> make_vec(size_t a) { return vector<T>(a); }
template<class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

//素因数分解O(√n)
map<ll,ll>prime_factor(ll n){
  map<ll,ll>res;
  for(ll i=2;i*i<=n;i++){
    while(n%i==0){
      res[i]++;
      n/=i;
    }
  }
  if(n!=1)res[n]=1;
  return res;
}

const ll MAX = 5000010;
long long fac[MAX], finv[MAX], inv[MAX];
//finvが階乗の逆元

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(ll n, ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

ll modpow(ll a, ll n,ll mod=MOD) {

    ll res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}

/*Eratosthenes()
ll N=2000010;
vl arr(N);
void Eratosthenes(){
  for(ll i = 0; i < N; i++){
    arr[i] = 1;
  }
        arr[1]=0;
  for(ll i = 2; i < sqrt(N); i++){
    if(arr[i]){
      for(ll j = 0; i * (j + 2) < N; j++){
        arr[i *(j + 2)] = 0;
      }
    }
  }
}*/
//素数判定O(√n)
bool is_prime(ll n){
  for(ll i=2;i*i<=n;i++){
    if(n%i==0)return false;
  }
  return n!=1;
}

//約数の列挙O(√n)
vector<ll>divisor(ll n){
  vector<ll>res;
  for(ll i=1;i*i<=n;i++){
    if(n%i==0){
      res.push_back(i);
      if(i != n/i) res.push_back(n/i);
    }
  }
  return res;
}


/* Trie 木: 文字の種類(char_size)、int型で0に対応する文字(base)
    insert(word): 単語 word を Trie 木に挿入する
    search(word): 単語 word が Trie 木にあるか判定する
    start_with(prefix):  prefix が一致する単語が Trie 木にあるか判定する
    count(): 挿入した単語の数を返す
    size(): Trie 木の頂点数を返す
    計算量:insert, search ともに O(M)(Mは単語の長さ)
*/
template <int char_size, int base>
struct Trie {
    struct Node {            // 頂点を表す構造体
        vector<int> next;    // 子の頂点番号を格納。存在しなければ-1
        vector<int> accept;  // 末端がこの頂点になる単語の word_id を保存
        int c;               // base からの間隔をint型で表現したもの
        int common;          // いくつの単語がこの頂点を共有しているか
        Node(int c_) : c(c_), common(0) {
            next.assign(char_size, -1);
        }
    };
    vector<Node> nodes;  // trie 木本体
    int root;
    Trie() : root(0) {
        nodes.push_back(Node(root));
    }
    // 単語の挿入
    void insert(const string &word, int word_id) {
        int node_id = 0;
        for (int i = 0; i < (int)word.size(); i++) {
            int c = (int)(word[i] - base);
            int &next_id = nodes[node_id].next[c];
            if (next_id == -1) {  // 次の頂点が存在しなければ追加
                next_id = (int)nodes.size();
                nodes.push_back(Node(c));
            }
            ++nodes[node_id].common;
            node_id = next_id;
        }
        ++nodes[node_id].common;
        nodes[node_id].accept.push_back(word_id);
    }
    void insert(const string &word) {
        insert(word, nodes[0].common);
    }
    // 単語とprefixの検索
    bool search(const string &word, bool prefix = false) {
        int node_id = 0;
        for (int i = 0; i < (int)word.size(); i++) {
            int c = (int)(word[i] - base);
            int &next_id = nodes[node_id].next[c];
            if (next_id == -1) {  // 次の頂点が存在しなければ終了
                return false;
            }
            node_id = next_id;
        }
        return (prefix) ? true : nodes[node_id].accept.size() > 0;
    }
    // prefix を持つ単語が存在するかの検索
    bool start_with(const string &prefix) {
        return search(prefix, true);
    }
    // 挿入した単語の数
    int count() const {
        return (nodes[0].common);
    }
    // Trie木のノード数
    int size() const {
        return ((int)nodes.size());
    }
};

// //Lowest Common Ancestor
// struct Edge{
//     int to;
//     Edge(int to):to(to){}
// };
 
// using Graph = vector<vector<Edge>>;
// class lca {
// public:
//     const int n = 0;
//     const int log2_n = 0;
//     vector<vector<int>> parent;
//     vector<int> depth;
 
//     lca() {}
   
//     //g:グラフ root:根
//     lca(const Graph &g, int root)
//         : n(g.size()), log2_n(log2(n) + 1), parent(log2_n, vector<int>(n)), depth(n) {
//         dfs(g, root, -1, 0);
//         for (int k = 0; k + 1 < log2_n; k++) {
//             for (int v = 0; v < (int)g.size(); v++) {
//                 if (parent[k][v] < 0)
//                     parent[k + 1][v] = -1;
//                 else
//                     parent[k + 1][v] = parent[k][parent[k][v]];
//             }
//         }
//     }
 
//     void dfs(const Graph &g, int v, int p, int d) {
//         parent[0][v] = p;
//         depth[v] = d;
//         for (auto &e : g[v]) {
//             if (e.to != p) dfs(g, e.to, v, d + 1);
//         }
//     }
//     //uとvのlcaを取得
//     int get(int u, int v) {
//         if (depth[u] > depth[v]) swap(u, v);
//         for (int k = 0; k < log2_n; k++) {
//             if ((depth[v] - depth[u]) >> k & 1) {
//                 v = parent[k][v];
//             }
//         }
//         if (u == v) return u;
//         for (int k = log2_n - 1; k >= 0; k--) {
//             if (parent[k][u] != parent[k][v]) {
//                 u = parent[k][u];
//                 v = parent[k][v];
//             }
//         }
//         return parent[0][u];
//     }
// 	int dep(int i) {
// 		return depth[i];
// 	}
//     int dist(int u,int v){
//         return depth[u]+depth[v]-depth[get(u,v)]*2;
//     }
// };

// union by size + path having
class UnionFind {
public:
    vector <ll> par; // 各元の親を表す配列
    vector <ll> siz; // 素集合のサイズを表す配列(1 で初期化)

    // Constructor
    UnionFind(ll sz_): par(sz_), siz(sz_, 1LL) {
        for (ll i = 0; i < sz_; ++i) par[i] = i; // 初期では親は自分自身
    }
    void init(ll sz_) {
        par.resize(sz_);
        siz.assign(sz_, 1LL);  // resize だとなぜか初期化されなかった
        for (ll i = 0; i < sz_; ++i) par[i] = i; // 初期では親は自分自身
    }

    // Member Function
    // Find
    ll root(ll x) { // 根の検索
        while (par[x] != x) {
            x = par[x] = par[par[x]]; // x の親の親を x の親とする
        }
        return x;
    }

    // Union(Unite, Merge)
    bool merge(ll x, ll y) {
        x = root(x);
        y = root(y);
        if (x == y) return false;
        // merge technique(データ構造をマージするテク.小を大にくっつける)
        if (siz[x] < siz[y]) swap(x, y);
        siz[x] += siz[y];
        par[y] = x;
        return true;
    }

    bool issame(ll x, ll y) { // 連結判定
        return root(x) == root(y);
    }

    ll size(ll x) { // 素集合のサイズ
        return siz[root(x)];
    }
};

// 0-indexed parmutation only
vvl cycle_partition(const vl &p){
    ll n=p.size();
    vvl ret;
    vector<bool> check(n,false);
    rep(i,n)if(!check[p[i]]){
        vl v;
        ll pos=p[i];
        v.pb(i);
        check[i]=true;
        while(pos!=i){
            v.pb(pos);
            check[pos]=true;
            pos=p[pos];
        }
        ret.pb(v);
    }
    return ret;
}

vl Z_algorithm(vl s){
    ll c=0,n=s.size();
    vl Z(n,0);
    for(ll i=1;i<n;i++){
        ll l=i-c;
        if(i+Z[l]<c+Z[c]){
            Z[i]=Z[l];
        }else{
            ll j=max(0LL,c+Z[c]-i);
            while(i+j<n && s[j]==s[i+j])j++;
            Z[i]=j;
            c=i;
        }
    }
    Z[0]=n;
    return Z;
}

//Manachar 修理中
// vl Manachar(string S){
//     ll c=0,n=S.size();
//     vl R(n,1);
//     for(ll i=0;i<n;i++){
//         ll l=c-(i-c);
//         if(i+R[l]<c+R[c]){
//             R[i]=R[l];
//         }else{
//             ll j=c+R[c]-i;
//             while(i-j>=0 && i+j<n && S[i-j] == S[i+j])j++;
//             R[i]=j;
//             c=i;
//         }
//     }
//     return R;
// }



template <typename T>
T pow(T a, long long n, T e = 1) {
    T ret = e;
    while (n) {
        if (n & 1) ret *= a;
        a *= a;
        n >>= 1;
    }
    return ret;
}
 
template <int mod>
struct ModInt {
    int x;
    ModInt() : x(0) {}
    ModInt(long long x_) {
        if ((x = x_ % mod + mod) >= mod) x -= mod;
    }
    ModInt& operator+=(ModInt rhs) {
        if ((x += rhs.x) >= mod) x -= mod;
        return *this;
    }
    ModInt& operator-=(ModInt rhs) {
        if ((x -= rhs.x) < 0) x += mod;
        return *this;
    }
    ModInt& operator*=(ModInt rhs) {
        x = (unsigned long long)x * rhs.x % mod;
        return *this;
    }
    ModInt& operator/=(ModInt rhs) {
        x = (unsigned long long)x * rhs.inv().x % mod;
        return *this;
    }
 
    ModInt operator-() const { return -x < 0 ? mod - x : -x; }
    ModInt operator+(ModInt rhs) const { return ModInt(*this) += rhs; }
    ModInt operator-(ModInt rhs) const { return ModInt(*this) -= rhs; }
    ModInt operator*(ModInt rhs) const { return ModInt(*this) *= rhs; }
    ModInt operator/(ModInt rhs) const { return ModInt(*this) /= rhs; }
    bool operator==(ModInt rhs) const { return x == rhs.x; }
    bool operator!=(ModInt rhs) const { return x != rhs.x; }
    ModInt inv() const { return pow(*this, mod - 2); }
 
    friend ostream& operator<<(ostream& s, ModInt<mod> a) {
        s << a.x;
        return s;
    }
    friend istream& operator>>(istream& s, ModInt<mod>& a) {
        s >> a.x;
        return s;
    }
};
 
using mint = ModInt<MOD>;
typedef vector<mint> vm;
typedef vector<vector<mint> >vvm;
typedef vector<vector<vector<mint> > >vvvm;

template <typename T>
struct segment_tree_beats{
  int N;
  vector<T> max1, max2, min1, min2, add, sum;
  vector<int> maxc, minc, len;
  void update_max(int i, T x){
    sum[i] += (x - max1[i]) * maxc[i];
    if (max1[i] == min1[i]){
      min1[i] = x;
    } else if (max1[i] == min2[i]){
      min2[i] = x;
    }
    max1[i] = x;
  }
  void update_min(int i, T x){
    sum[i] += (x - min1[i]) * minc[i];
    if (min1[i] == max1[i]){
      max1[i] = x;
    } else if (min1[i] == max2[i]){
      max2[i] = x;
    }
    min1[i] = x;
  }
  void update_add(int i, T x){
    max1[i] += x;
    if (max2[i] != -INF){
      max2[i] += x;
    }
    min1[i] += x;
    if (min2[i] != INF){
      min2[i] += x;
    }
    sum[i] += x * len[i];
    add[i] += x;
  }
  void push(int i){
    if (i >= N - 1){
      return;
    }
    int l = i * 2 + 1;
    int r = i * 2 + 2;
    if (add[i] != 0){
      update_add(l, add[i]);
      update_add(r, add[i]);
      add[i] = 0;
    }
    if (max1[i] < max1[l]){
      update_max(l, max1[i]);
    }
    if (min1[i] > min1[l]){
      update_min(l, min1[i]);
    }
    if (max1[i] < max1[r]){
      update_max(r, max1[i]);
    }
    if (min1[i] > min1[r]){
      update_min(r, min1[i]);
    }
  }
  void update(int i){
    int l = i * 2 + 1;
    int r = i * 2 + 2;
    sum[i] = sum[l] + sum[r];
    if (max1[l] > max1[r]){
      max1[i] = max1[l];
      max2[i] = max(max2[l], max1[r]);
      maxc[i] = maxc[l];
    } else if (max1[l] < max1[r]){
      max1[i] = max1[r];
      max2[i] = max(max1[l], max2[r]);
      maxc[i] = maxc[r];
    } else {
      max1[i] = max1[l];
      max2[i] = max(max2[l], max2[r]);
      maxc[i] = maxc[l] + maxc[r];
    }
    if (min1[l] < min1[r]){
      min1[i] = min1[l];
      min2[i] = min(min2[l], min1[r]);
      minc[i] = minc[l];
    } else if (min1[l] > min1[r]){
      min1[i] = min1[r];
      min2[i] = min(min1[l], min2[r]);
      minc[i] = minc[r];
    } else {
      min1[i] = min1[l];
      min2[i] = min(min2[l], min2[r]);
      minc[i] = minc[l] + minc[r];
    }
  }
  segment_tree_beats(vector<T> A){
    int n = A.size();
    N = 1;
    while (N < n){
      N *= 2;
    }
    max1 = vector<T>(N * 2 - 1, -INF);
    max2 = vector<T>(N * 2 - 1, -INF);
    min1 = vector<T>(N * 2 - 1, INF);
    min2 = vector<T>(N * 2 - 1, INF);
    add = vector<T>(N * 2 - 1, 0);
    sum = vector<T>(N * 2 - 1, 0);
    maxc = vector<int>(N * 2 - 1, 1);
    minc = vector<int>(N * 2 - 1, 1);
    len = vector<int>(N * 2 - 1, 1);
    for (int i = 0; i < n; i++){
      max1[N - 1 + i] = A[i];
      min1[N - 1 + i] = A[i];
      sum[N - 1 + i] = A[i];
    }
    for (int i = N - 2; i >= 0; i--){
      len[i] = len[i * 2 + 1] + len[i * 2 + 2];
      update(i);
    }
  }
  void range_chmin(int L, int R, T x, int i, int l, int r){
    if (r <= L || R <= l || x >= max1[i]){
      return;
    } else if (L <= l && r <= R && x > max2[i]){
      update_max(i, x);
      return;
    }
    push(i);
    int m = (l + r) / 2;
    range_chmin(L, R, x, i * 2 + 1, l, m);
    range_chmin(L, R, x, i * 2 + 2, m, r);
    update(i);
  }
  void range_chmax(int L, int R, T x, int i, int l, int r){
    if (r <= L || R <= l || x <= min1[i]){
      return;
    } else if (L <= l && r <= R && x < min2[i]){
      update_min(i, x);
      return;
    }
    push(i);
    int m = (l + r) / 2;
    range_chmax(L, R, x, i * 2 + 1, l, m);
    range_chmax(L, R, x, i * 2 + 2, m, r);
    update(i);
  }
  void range_add(int L, int R, T x, int i, int l, int r){
    if (r <= L || R <= l){
      return;
    } else if (L <= l && r <= R){
      update_add(i, x);
      return;
    }
    push(i);
    int m = (l + r) / 2;
    range_add(L, R, x, i * 2 + 1, l, m);
    range_add(L, R, x, i * 2 + 2, m, r);
    update(i);
  }
  T range_sum(int L, int R, int i, int l, int r){
    if (r <= L || R <= l){
      return 0;
    } else if (L <= l && r <= R){
      return sum[i];
    }
    push(i);
    int m = (l + r) / 2;
    return range_sum(L, R, i * 2 + 1, l, m) +	range_sum(L, R, i * 2 + 2, m, r);
  }
  void range_chmin(int L, int R, T x){
    range_chmin(L, R, x, 0, 0, N);
  }
  void range_chmax(int L, int R, T x){
    range_chmax(L, R, x, 0, 0, N);
  }
  void range_add(int L, int R, T x){
    range_add(L, R, x, 0, 0, N);
  }
  T range_sum(int L, int R){
    return range_sum(L, R, 0, 0, N);
  }
};

struct PartiallyPersistentUnionFind {
    vector<ll> par, last;
    vector<vector<P> > history;
    
    PartiallyPersistentUnionFind(ll n) : par(n, -1), last(n, -1), history(n) {
        for (auto &vec : history) vec.emplace_back(-1, -1);
    }
    void init(ll n) {
        par.assign(n, -1); last.assign(n, -1); history.assign(n, vector<P>());
        for (auto &vec : history) vec.emplace_back(-1, -1);
    }
    
    ll root(ll t, ll x) {
        if (last[x] == -1 || t < last[x]) return x;
        return root(t, par[x]);
    }
    
    bool issame(ll t, ll x, ll y) {
        return root(t, x) == root(t, y);
    }
    
    bool merge(ll t, ll x, ll y) {
        x = root(t, x); y = root(t, y);
        if (x == y) return false;
        if (par[x] > par[y]) swap(x, y); // merge technique
        par[x] += par[y];
        par[y] = x;
        last[y] = t;
        history[x].emplace_back(t, par[x]);
        return true;
    }
    
    ll size(ll t, ll x) {
        x = root(t, x);
        return -prev(lower_bound(history[x].begin(), history[x].end(), make_pair(t, 0LL)))->second;
    }
};

// matrix
template<class T> struct Matrix {
    vector<vector<T> > val;
    Matrix(int n = 1, int m = 1, T v = 0) : val(n, vector<T>(m, v)) {}
    void init(int n, int m, T v = 0) {val.assign(n, vector<T>(m, v));}
    void resize(int n, int m) {
        val.resize(n);
        for (int i = 0; i < n; ++i) val[i].resize(m);
    }
    Matrix<T>& operator = (const Matrix<T> &A) {
        val = A.val;
        return *this;
    }
    size_t size() const {return val.size();}
    vector<T>& operator [] (int i) {return val[i];}
    const vector<T>& operator [] (int i) const {return val[i];}
    friend ostream& operator << (ostream& s, const Matrix<T>& M) {
        s << endl;
        for (int i = 0; i < (int)M.size(); ++i) s << M[i] << endl;
        return s;
    }
};

template<class T> Matrix<T> operator * (const Matrix<T> &A, const Matrix<T> &B) {
    Matrix<T> R(A.size(), B[0].size());
    for (int i = 0; i < A.size(); ++i)
        for (int j = 0; j < B[0].size(); ++j)
            for (int k = 0; k < B.size(); ++k)
                R[i][j] += A[i][k] * B[k][j];
    return R;
}

template<class T> Matrix<T> pow(const Matrix<T> &A, long long n) {
    Matrix<T> R(A.size(), A.size());
    auto B = A;
    for (int i = 0; i < A.size(); ++i) R[i][i] = 1;
    while (n > 0) {
        if (n & 1) R = R * B;
        B = B * B;
        n >>= 1;
    }
    return R;
}

template<class T> vector<T> operator * (const Matrix<T> &A, const vector<T> &B) {
    vector<T> v(A.size());
    for (int i = 0; i < A.size(); ++i)
        for (int k = 0; k < B.size(); ++k)
            v[i] += A[i][k] * B[k];
    return v;
}

template<class T> Matrix<T> operator + (const Matrix<T> &A, const Matrix<T> &B) {
    Matrix<T> R(A.size(), A[0].size());
    for (int i = 0; i < A.size(); ++i)
        for (int j = 0; j < A[0].size(); ++j)
            R[i][j] = A[i][j] + B[i][j];
    return R;
}

template<class T> Matrix<T> operator - (const Matrix<T> &A, const Matrix<T> &B) {
    Matrix<T> R(A.size(), A[0].size());
    for (int i = 0; i < A.size(); ++i)
        for (int j = 0; j < A[0].size(); ++j)
            R[i][j] = A[i][j] - B[i][j];
    return R;
}

const int MAX_ROW = 510; // to be set appropriately
const int MAX_COL = 510; // to be set appropriately
struct BitMatrix {
    int H, W;
    bitset<MAX_COL> val[MAX_ROW];
    BitMatrix(int m = 1, int n = 1) : H(m), W(n) {}
    inline bitset<MAX_COL>& operator [] (int i) {return val[i];}
};

int GaussJordan(BitMatrix &A, bool is_extended = false) {
    int rank = 0;
    for (int col = 0; col < A.W; ++col) {
        if (is_extended && col == A.W - 1) break;
        int pivot = -1;
        for (int row = rank; row < A.H; ++row) {
            if (A[row][col]) {
                pivot = row;
                break;
            }
        }
        if (pivot == -1) continue;
        swap(A[pivot], A[rank]);
        for (int row = 0; row < A.H; ++row) {
            if (row != rank && A[row][col]) A[row] ^= A[rank];
        }
        ++rank;
    }
    return rank;
}

int linear_equation(BitMatrix A, vector<int> b, vector<int> &res) {
    int m = A.H, n = A.W;
    BitMatrix M(m, n + 1);
    for (int i = 0; i < m; ++i) {
        for (int j = 0; j < n; ++j) M[i][j] = A[i][j];
        M[i][n] = b[i];
    }
    int rank = GaussJordan(M, true);

    // check if it has no solution
    for (int row = rank; row < m; ++row) if (M[row][n]) return -1;

    // answer
    res.assign(n, 0);
    for (int i = 0; i < rank; ++i) res[i] = M[i][n];
    return rank;
}


ll exp(ll n,ll r){
    if(r==0)return 1;
    return n*exp(n,r-1);
}

ll factorial(int n){
    if(n==0)return 1;
    return n*factorial(n-1);
}


void input_vvi(int n){
    vector<string>s(n);
    string ans;
    ans+="vector<vector<int>> dp={";
    rep(i,n){
        cin>>s[i];
        ans+="{";
        ans+=s[i];
        ans+="}";
        if(i!=n-1)ans+=",";
    }
    ans+="};";
    cout<<ans<<endl;
}

/**
 * @brief Rolling-Hash(ローリングハッシュ)
 * @see https://qiita.com/keymoon/items/11fac5627672a6d6a9f6
 * @docs docs/rolling-hash.md
 */
struct RollingHash {
  static const uint64_t mod = (1ull << 61ull) - 1;
  using uint128_t = __uint128_t;
  vector< uint64_t > power;
  const uint64_t base;

  static inline uint64_t add(uint64_t a, uint64_t b) {
    if((a += b) >= mod) a -= mod;
    return a;
  }

  static inline uint64_t mul(uint64_t a, uint64_t b) {
    uint128_t c = (uint128_t) a * b;
    return add(c >> 61, c & mod);
  }

  static inline uint64_t generate_base() {
    mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
    uniform_int_distribution< uint64_t > rand(1, RollingHash::mod - 1);
    return rand(mt);
  }

  inline void expand(size_t sz) {
    if(power.size() < sz + 1) {
      int pre_sz = (int) power.size();
      power.resize(sz + 1);
      for(int i = pre_sz - 1; i < sz; i++) {
        power[i + 1] = mul(power[i], base);
      }
    }
  }

  explicit RollingHash(uint64_t base = generate_base()) : base(base), power{1} {}

  vector< uint64_t > build(const string &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  template< typename T >
  vector< uint64_t > build(const vector< T > &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for(int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  uint64_t query(const vector< uint64_t > &s, int l, int r) {
    expand(r - l);
    return add(s[r], mod - mul(s[l], power[r - l]));
  }

  uint64_t combine(uint64_t h1, uint64_t h2, size_t h2len) {
    expand(h2len);
    return add(mul(h1, power[h2len]), h2);
  }

  int lcp(const vector< uint64_t > &a, int l1, int r1, const vector< uint64_t > &b, int l2, int r2) {
    int len = min(r1 - l1, r2 - l2);
    int low = 0, high = len + 1;
    while(high - low > 1) {
      int mid = (low + high) / 2;
      if(query(a, l1, l1 + mid) == query(b, l2, l2 + mid)) low = mid;
      else high = mid;
    }
    return low;
  }
};

struct SuccinctIndexableDictionary {
  size_t length;
  size_t blocks;
  vector< unsigned > bit, sum;

  SuccinctIndexableDictionary() = default;

  SuccinctIndexableDictionary(size_t length) : length(length), blocks((length + 31) >> 5) {
    bit.assign(blocks, 0U);
    sum.assign(blocks, 0U);
  }

  void set(int k) {
    bit[k >> 5] |= 1U << (k & 31);
  }

  void build() {
    sum[0] = 0U;
    for(int i = 1; i < blocks; i++) {
      sum[i] = sum[i - 1] + __builtin_popcount(bit[i - 1]);
    }
  }

  bool operator[](int k) {
    return (bool((bit[k >> 5] >> (k & 31)) & 1));
  }

  int rank(int k) {
    return (sum[k >> 5] + __builtin_popcount(bit[k >> 5] & ((1U << (k & 31)) - 1)));
  }

  int rank(bool val, int k) {
    return (val ? rank(k) : k - rank(k));
  }
};

/*
 * @brief Wavelet-Matrix(ウェーブレット行列)
 * @docs docs/wavelet-matrix.md
 */
template< typename T, int MAXLOG >
struct WaveletMatrix {
  size_t length;
  SuccinctIndexableDictionary matrix[MAXLOG];
  int mid[MAXLOG];

  WaveletMatrix() = default;

  WaveletMatrix(vector< T > v) : length(v.size()) {
    vector< T > l(length), r(length);
    for(int level = MAXLOG - 1; level >= 0; level--) {
      matrix[level] = SuccinctIndexableDictionary(length + 1);
      int left = 0, right = 0;
      for(int i = 0; i < length; i++) {
        if(((v[i] >> level) & 1)) {
          matrix[level].set(i);
          r[right++] = v[i];
        } else {
          l[left++] = v[i];
        }
      }
      mid[level] = left;
      matrix[level].build();
      v.swap(l);
      for(int i = 0; i < right; i++) {
        v[left + i] = r[i];
      }
    }
  }

  pair< int, int > succ(bool f, int l, int r, int level) {
    return {matrix[level].rank(f, l) + mid[level] * f, matrix[level].rank(f, r) + mid[level] * f};
  }

  // v[k]
  T access(int k) {
    T ret = 0;
    for(int level = MAXLOG - 1; level >= 0; level--) {
      bool f = matrix[level][k];
      if(f) ret |= T(1) << level;
      k = matrix[level].rank(f, k) + mid[level] * f;
    }
    return ret;
  }

  T operator[](const int &k) {
    return access(k);
  }

  // count i s.t. (0 <= i < r) && v[i] == x
  int rank(const T &x, int r) {
    int l = 0;
    for(int level = MAXLOG - 1; level >= 0; level--) {
      tie(l, r) = succ((x >> level) & 1, l, r, level);
    }
    return r - l;
  }

  // k-th(0-indexed) smallest number in v[l,r)
  T kth_smallest(int l, int r, int k) {
    assert(0 <= k && k < r - l);
    T ret = 0;
    for(int level = MAXLOG - 1; level >= 0; level--) {
      int cnt = matrix[level].rank(false, r) - matrix[level].rank(false, l);
      bool f = cnt <= k;
      if(f) {
        ret |= T(1) << level;
        k -= cnt;
      }
      tie(l, r) = succ(f, l, r, level);
    }
    return ret;
  }

  // k-th(0-indexed) largest number in v[l,r)
  T kth_largest(int l, int r, int k) {
    return kth_smallest(l, r, r - l - k - 1);
  }

  // count i s.t. (l <= i < r) && (v[i] < upper)
  int range_freq(int l, int r, T upper) {
    int ret = 0;
    for(int level = MAXLOG - 1; level >= 0; level--) {
      bool f = ((upper >> level) & 1);
      if(f) ret += matrix[level].rank(false, r) - matrix[level].rank(false, l);
      tie(l, r) = succ(f, l, r, level);
    }
    return ret;
  }

  // count i s.t. (l <= i < r) && (lower <= v[i] < upper)
  int range_freq(int l, int r, T lower, T upper) {
    return range_freq(l, r, upper) - range_freq(l, r, lower);
  }

  // max v[i] s.t. (l <= i < r) && (v[i] < upper)
  T prev_value(int l, int r, T upper) {
    int cnt = range_freq(l, r, upper);
    return cnt == 0 ? T(-1) : kth_smallest(l, r, cnt - 1);
  }

  // min v[i] s.t. (l <= i < r) && (lower <= v[i])
  T next_value(int l, int r, T lower) {
    int cnt = range_freq(l, r, lower);
    return cnt == r - l ? T(-1) : kth_smallest(l, r, cnt);
  }
};

template< typename T, int MAXLOG >
struct CompressedWaveletMatrix {
  WaveletMatrix< int, MAXLOG > mat;
  vector< T > ys;

  CompressedWaveletMatrix(const vector< T > &v) : ys(v) {
    sort(begin(ys), end(ys));
    ys.erase(unique(begin(ys), end(ys)), end(ys));
    vector< int > t(v.size());
    for(int i = 0; i < v.size(); i++) t[i] = get(v[i]);
    mat = WaveletMatrix< int, MAXLOG >(t);
  }

  inline int get(const T& x) {
    return lower_bound(begin(ys), end(ys), x) - begin(ys);
  }

  T access(int k) {
    return ys[mat.access(k)];
  }

  T operator[](const int &k) {
    return access(k);
  }

  int rank(const T &x, int r) {
    auto pos = get(x);
    if(pos == ys.size() || ys[pos] != x) return 0;
    return mat.rank(pos, r);
  }

  T kth_smallest(int l, int r, int k) {
    return ys[mat.kth_smallest(l, r, k)];
  }

  T kth_largest(int l, int r, int k) {
    return ys[mat.kth_largest(l, r, k)];
  }

  int range_freq(int l, int r, T upper) {
    return mat.range_freq(l, r, get(upper));
  }

  int range_freq(int l, int r, T lower, T upper) {
    return mat.range_freq(l, r, get(lower), get(upper));
  }

  T prev_value(int l, int r, T upper) {
    auto ret = mat.prev_value(l, r, get(upper));
    return ret == -1 ? T(-1) : ys[ret];
  }

  T next_value(int l, int r, T lower) {
    auto ret = mat.next_value(l, r, get(lower));
    return ret == -1 ? T(-1) : ys[ret];
  }
};


pair<long long,long long>roop_search(vl next_index,ll first_point){
	ll idx=first_point;
	map<ll,ll>mp;
	mp[idx]=0;
	ll cur=1;
	ll roop_begin=-1;
	ll roop_size=-1;
	while(true){
		idx=next_index[idx];
		if(mp.count(idx)){
			roop_begin=mp[idx];
			roop_size=cur-roop_begin;
			break;
		}
		mp[idx]=cur++;
	}
	return {roop_begin,roop_size};
}

ll functional(ll x){
    if(x==0)return 1;
    else return x*functional(x-1);
}


int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    cout << fixed << setprecision(13);
    //CDEは制約を読もう!
    //主客転倒!二重和のときは一番内側の物が何回使われるか
    //√Nで分けるテク
    //絶対値は外して2通りの式にした後、変数ごとにまとめる
    //組み合わせが少ないそうなものはdfsで実行してみる(典型25)
    /*--------------------------------*/

    double a;cin>>a;
    a/=3;
    cout<<a*a*sqrt(3)/4<<endl;

}
0