#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 200010, INF = 0x3f3f3f3f;

int n, f[N], ma;

int main() {
    scanf("%d", &n);
    memset(f, 0x3f, sizeof(f));
    ma = 0;
    for (int i = 1, x, idx; i <= n; ++i) {
        scanf("%d", &x);
        if (x >= i) {
            idx = upper_bound(f + 1, f + n + 1, x - i) - f;
            f[idx] = x - i;
            ma = max(ma, idx);
        }
    }
    printf("%d\n", n - ma);
    
    return 0;
}