A - 1 CodeForces - 691A（题意）

According to rules of the Berland fashion, a jacket should be fastened by all the buttons except only one, but not necessarily it should be the last one. Also if the jacket has only one button, it should be fastened, so the jacket will not swinging open.

You are given a jacket with n buttons. Determine if it is fastened in a right way.

Input
The first line contains integer n (1 ≤ n ≤ 1000) — the number of buttons on the jacket.

The second line contains n integers ai (0 ≤ ai ≤ 1). The number ai = 0 if the i-th button is not fastened. Otherwise ai = 1.

Output
In the only line print the word “YES” if the jacket is fastened in a right way. Otherwise print the word “NO”.

Examples
Input
3
1 0 1
Output
YES
Input
3
1 0 0
Output
NO
题意：只能放n - 1个纽扣，n为1的时候放1个。
思路：题目什么鬼？？？猜了个意思上去就a了。。。

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int ans = 0;
    for(int i = 1;i <= n;i++)
    {
        int x;
        cin>>x;
        ans += x;
        if(n == 1 && x == 1)
        {
            printf("YES\n");
            return 0;
        }
        else if(n == 1 && x != 1)
        {
            printf("NO\n");
            return 0;
        }
    }
    if(ans == n - 1)
    {
        printf("YES\n");
        return 0;
    }
    else
        printf("NO\n");
    return 0;
}