#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  int cnt = 0, val;
  for (int k = 0; k < n; k++) {
    cin >> val;
    cnt += val;
  }
  if (n == 1 && val == 1)
    cout << "YES";
  else if (cnt == n - 1 && n != 1)
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
