#include <bits/stdc++.h> using namespace std; using ll= long long; using ld= long double; using i128= __int128; using pll= pair<ll, ll>; using vi= vector<int>; using vl= vector<ll>; using vd= vector<ld>; using vs= vector<string>; using vi128= vector<i128>; using vb= vector<bool>; using vpll= vector<pll>; using vvi= vector<vi>; using vvl= vector<vl>; using vvd= vector<vd>; using vvs= vector<vs>; using vvi128= vector<vi128>; using vvb= vector<vb>; using vvpll= vector<vpll>; // using mint = modint998244353; constexpr ll mod= 1e9 + 7; // constexpr ll mod= 998244353; #define ALL(x) (x).begin(), (x).end() #define _overload(_1, _2, _3, name, ...) name #define REPBASE(i, a, b) for(ll(i)= (a); (i) < (b); (i)++) #define RREPBASE(i, a, b) for(ll(i)= (a); (i) >= (b); (i)--) #define REPB(i, n) REPBASE(i, 0, n) #define REPS(i, n) REPBASE(i, 1, n + 1) #define RREP(i, n) RREPBASE(i, n - 1, 0) #define RREPS(i, n) RREPBASE(i, n, 1) #define REP(...) _overload(__VA_ARGS__, REPBASE, REPB)(__VA_ARGS__) #define EACH(x, c) for(auto &x : c) #define pb push_back #define eb emplace_back #define mp make_pair #define fi first #define se second #define UNIQUE(v) v.erase(unique(ALL(v)), v.end()) #define YES(n) ((n) ? "YES" : "NO") #define Yes(n) ((n) ? "Yes" : "No") #define yes(n) ((n) ? "yes" : "no") #define SZ(x) ((ll)(x).size()) #define BIT(n) (1LL << (n)) template <class T> inline bool chmax(T &a, const T &b) { if(a < b) { a= b; return 1; } return 0; } template <class T> inline bool chmin(T &a, const T &b) { if(b < a) { a= b; return 1; } return 0; } signed main() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(12); ld ans = 0; ll k; cin >> k; REP(i,k){ ans += (ld)1 / (1 + i); } ans /= k; if(k == 0){ ans = atan((ld)1)*atan((ld)1)*(ld)8/(ld)3; } cout << ans << "\n"; }