#include <iostream>
#include <algorithm>

using namespace std;

const int N = 200010;

int n, a[N], dp[N], ans;

int main() {
    // freopen("score.in", "r", stdin);
    // freopen("score.out", "w", stdout);

    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) scanf("%d", &a[i]);

    for (int i = 1; i <= n; ++i) {
        if (a[i] >= i) {
            int idx = upper_bound(dp + 1, dp + ans + 1, a[i] - i) - dp;
            dp[idx] = a[i] - i;
            ans = max(ans, idx);
        }
    }

    printf("%d\n", n - ans);

    return 0;
}