#include <iostream>
using namespace std;

int n;
int a[100010], a1[100010], a2[100010];
int b[100010], c[100010];
int f[100010] = { 0 }, g[100010];
int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i], a1[i] = a[i] - i, a2[i] = a[i] + i;
    int len = 0;
    for (int i = 1; i <= n; i++) {
        if (len == 0 || a1[i] >= a1[f[len]])
            f[++len] = i;
        else {
            int l = 1, r = len;
            while (l <= r) {
                int mid = (l + r) >> 1;
                if (a1[f[mid]] <= a1[i])
                    l = mid + 1;
                else
                    r = mid - 1;
            }
            f[l] = i;
        }
        b[i] = len;
    }
    len = 0;
    for (int i = n; i >= 1; i--) {
        if (len == 0 || a2[i] >= a2[g[len]])
            g[++len] = i;
        else {
            int l = 1, r = len;
            while (l <= r) {
                int mid = (l + r) >> 1;
                if (a2[g[mid]] <= a2[i])
                    l = mid + 1;
                else
                    r = mid - 1;
            }
            g[l] = i;
        }
        c[i] = len;
    }
    int ans = 1e9;
    for (int i = 1; i < n; i++) ans = min(ans, n - b[i] - c[i + 1]);
    cout << ans << endl;
    system("pause");
    return 0;
}

/sandbox/1/a.cpp: In function 'int main()':
/sandbox/1/a.cpp:57:5: error: 'system' was not declared in this scope
   57 |     system("pause");
      |     ^~~~~~