#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  cout << ((n == 1 && a[0] == 1 || n > 1 && count(a.begin(), a.end(), 0) == 1)
               ? "YES"
               : "NO")
       << endl;
}
