#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, check = 0;
  string x;
  cin >> n >> x;
  sort(x.begin(), x.end());
  if (n == 1)
    cout << "YES";
  else {
    for (int i = 0; i < x.size() - 1; i++) {
      if (x[i] == x[i + 1]) {
        check = 1;
        break;
      }
    }
    if (check == 1)
      cout << "YES";
    else
      cout << "NO";
  }
  return 0;
}
