#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a[100 + 10], t = 0;
  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;
      t++;
    }
  }
  if (t == 0) {
    cout << "NO" << endl;
  }
}
