#include <bits/stdc++.h>
using namespace std;
int main() {
  int a;
  char c[101010], d = 'a';
  cin >> a >> c;
  if (a == 1) {
    cout << "YES" << endl;
    return 0;
  }
  for (int i = 0; i < 26; i++) {
    if (count(c, c + a, d++) > 1) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
}
