#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m = 0;
  cin >> n;
  int last;
  for (int(i) = 0; (i) < (n); ++(i)) {
    cin >> last;
    m += last;
  }
  cout << ((n - m == 1 && n > 1) || (n == 1 && m == 1) ? "YES\n" : "NO\n");
}
