#include using namespace std; #define rep(i,n) for(ll i=0;i=0;i--) #define perl(i,r,l) for(ll i=r-1;i>=l;i--) #define fi first #define se second #define pb push_back #define ins insert #define pqueue(x) priority_queue,greater> #define all(x) (x).begin(),(x).end() #define CST(x) cout<; using vvl=vector>; using pl=pair; using vpl=vector; using vvpl=vector; const ll MOD=1000000007; const ll MOD9=998244353; const int inf=1e9+10; const ll INF=4e18; const ll dy[8]={1,0,-1,0,1,1,-1,-1}; const ll dx[8]={0,1,0,-1,1,-1,1,-1}; template inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false)); } template inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false)); } //0-indexed,2冪のセグメントツリー template struct SegTree { private: int n;// 葉の数 vector data;// データを格納するvector T def; // 初期値かつ単位元 function operation; // 区間クエリで使う処理 function change;// 点更新で使う処理 T find(int a, int b) { T val_left = def, val_right = def; for (a += (n - 1), b += (n - 1); a < b; a >>= 1, b >>= 1) { if ((a & 1) == 0){ val_left = operation(val_left, data[a]); } if ((b & 1) == 0){ val_right = operation(data[--b],val_right); } } return operation(val_left, val_right); } public: // _n:必要サイズ, _def:初期値かつ単位元, _operation:クエリ関数, // _change:更新関数 SegTree(size_t _n, T _def, function _operation, function _change=[](T a,T b){return b;}) : def(_def), operation(_operation), change(_change) { n = 1; while (n < _n) { n *= 2; } data = vector(2 * n - 1, def); } void set(int i, T x) { data[i + n - 1] = x; } void build() { for (int k=n-2;k>=0;k--) data[k] = operation(data[2*k+1],data[2*k+2]); } // 場所i(0-indexed)の値をxで更新 void update(int i, T x) { i += n - 1; data[i] = change(data[i], x); while (i > 0) { i = (i - 1) / 2; data[i] = operation(data[i * 2 + 1], data[i * 2 + 2]); } } T all_prod(){ return data[0]; } // [a, b)の区間クエリを実行 T query(int a, int b) { //return _query(a, b, 0, 0, n); return find(a,b); } // 添字でアクセス T operator[](int i) { return data[i + n - 1]; } }; int main(){ ll n;cin >> n; vl a(n);rep(i,n)cin >> a[i]; vpl pls(n); rep(i,n)pls[i]=make_pair(a[i]-i,i); pls.push_back(make_pair(-INF,-INF)); sort(all(pls)); vl inv(n);rep(i,n)inv[pls[i+1].second]=i+1; SegTree st(n+1,INF,[](ll a,ll b){return min(a,b);}); st.update(0,1); rep(i,n){ ll q=st.query(0,inv[i])+i-1; st.update(inv[i],q-i); } ll ans=INF; rep(i,n){ chmin(ans,st[inv[i]]+n-1); } cout << ans << endl; }