#include <bits/stdc++.h>   using namespace std;   int main() {     int n, ans = 0, c;     cin >> n;     for (long long i = 1; i <= n; i++) {       cin >> c;       ans += c;     }     c = (n == 1 ? 1 : n - 1);     if (ans == c)       cout <<  YES ;     else       cout <<  NO ;     return 0;   }   