#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[110], n;
  while (cin >> n) {
    for (int i = 0; i < n; i++) cin >> a[i];
    sort(a, a + n);
    for (int i = 1; i < n; i++) {
      if (a[i] != a[i - 1]) {
        cout << a[i] << endl;
        return 0;
      }
    }
    puts("NO");
  }
  return 0;
}
