#include <bits/stdc++.h>
int main() {
  int check[26] = {0};
  int n;
  char alpha[100005];
  scanf("%d", &n);
  getchar();
  gets(alpha);
  for (int i = 0; i < n; i++) {
    check[alpha[i] - 'a']++;
    if (check[alpha[i] - 'a'] > 1) {
      printf("YES");
      return 0;
    }
  }
  if (n == 1)
    printf("YES");
  else
    printf("NO");
  return 0;
}
