#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef long long ll;

int N;
int A[200000];

int dp[200005];
const int INF = 2e9;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    cin >> N;
    for(int i = 0; i <= N; i++){
        dp[i] = INF;
    }
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        A[i] -= i;
    }
    for(int i = 0; i < N; i++){
        if(A[i] <= 0) continue;
        auto p = upper_bound(dp, dp+N+1, A[i]);
        *p = min(A[i], *p);
    }
    int ans = 0;
    for(int i = 0; i < N; i++){
        if(dp[i] != INF) ans = i+1;
    }
    cout << N-ans << endl;
}