A 了前 5 个点。

#include <bits/stdc++.h>
using namespace std;
#define int long long
int a[100010], ans = 1e18;
signed main() {
	ios::sync_with_stdio(false);
	ios_base::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	while (a[n] == 0 && n > 0) {
		n--;
	}
	int cnt = 0, res = 0;
	for (int i = 1; i <= n; i++) {
		if (a[i] == 0) {
			cnt++;
			res++;
		} else {
			if (cnt > a[i]) {
				ans = min(ans, cnt - a[i]);
			} else {
				ans = 1e18;
			}
		}
	}
	if (ans != 1e18)
		n -= ans;
	cout << n;
	return 0;
}