#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string sentence;
  cin >> sentence;
  map<char, int> m;
  for (int i = 97; i < 123; i++) m[(char)i] = 0;
  for (int i = 0; i < n; i++) {
    m[tolower(sentence[i])] = 1;
  }
  for (auto x : m) {
    if (x.second == 0) {
      cout << "NO";
      return 0;
    }
  }
  cout << "YES";
}
