#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int N;
int A[200000];
int LIS[200002];

int main() {
    cin >> N;
    rep(i, N) cin >> A[i];
    rep(i, N) A[i] -= i;
    rep(i, N + 2) LIS[i] = 2000000000;
    LIS[0] = -2000000000;
    rep(i, N) {
        if (A[i] < 0) continue;
        auto p = upper_bound(LIS, LIS + N + 2, A[i]);
        *p = A[i];
    }
    int ans = 0;
    rep(i, N + 1) if (LIS[i] != 2000000000) ans = i;
    ans = N - ans;
    cout << ans << endl;
    return 0;
}