#include <bits/stdc++.h>
using namespace std;
int n;
int a[1005];
int main() {
  cin >> n;
  int x;
  int ans = 0;
  if (n == 1) {
    cin >> x;
    if (x)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    cin >> x;
    ans += x;
  }
  if (ans == n - 1)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
