#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s;
  cin >> n >> s;
  for (int i = 0; i < n - 1; ++i) {
    if (s[i] > s[i + 1]) {
      cout << "YES" << endl;
      cout << s[i + 1] << ' ' << s[i + 2] << endl;
    }
  }
  cout << "NO" << endl;
  return 0;
}
