#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 7;
const long long LL_INF = 1ll * INF * INF;
const int MAX_N = 500000 + 7;
const int mod = INF;
template <typename T>
inline void addmod(T& a, const long long& b, const int& MOD = mod) {
  a = (a + b) % MOD;
  if (a < 0) a += MOD;
}
void solve() {
  int n;
  string s;
  cin >> n >> s;
  sort(s.begin(), s.end());
  for (int i = 1; i < s.size(); ++i) {
    if (s[i] == s[i - 1]) {
      cout << "YES";
      return;
    }
  }
  if (s.size() == 1)
    cout << "YES";
  else
    cout << "NO";
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  const bool multiple_test = false;
  int test = 1;
  if (multiple_test) cin >> test;
  for (int i = 0; i < test; ++i) {
    solve();
  }
}
