#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 7, SIZE = 1e5 + 3, MOD = 2e9 + 11, P = 37;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << fixed;
  cout.precision(9);
  int n;
  string s;
  cin >> n >> s;
  vector<bool> used(26, false);
  for (auto &i : s) i = i | ' ';
  for (auto i : s) {
    used[i - 'a'] = true;
  }
  if (*min_element(used.begin(), used.end()))
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
