#include <bits/stdc++.h>
using namespace std;
int main() {
  long n;
  cin >> n;
  string s;
  cin >> s;
  long a[26] = {0};
  for (long i = 0; i < n; i++) {
    a[s[i] - 'a']++;
  }
  int f = 0;
  for (long i = 0; i < 26; i++) {
    if (a[i] >= 2) {
      f = 1;
      break;
    }
  }
  if (s.size() == 1) {
    f = 1;
  }
  if (f) {
    cout << "YES";
  } else
    cout << "NO";
}
