#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int sum = 0;
  for (int i = 1; i <= n; i++) {
    int a;
    cin >> a;
    sum += a;
  }
  if ((n == 1 && sum == 1) || (n > 1 && sum == n - 1)) {
    cout << "YES";
  } else {
    cout << "NO";
  }
  return 0;
}
