python 测试点有问题，限 c++

#include <iostream>
using namespace std;
int main() {
    int n, m;
    cin >> n;
    int ans = 0, sum = 0;
    for (int i = 1; i < n; i++) {
        cin >> m;
        sum += m;
        ans += i;
    }

    cout << ans + n - sum;
}