#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i = 0;
  string frase;
  vector<int> vetor(26);
  int flag = 1;
  cin >> n;
  cin >> frase;
  if (n < 26)
    cout << "NO\n";
  else {
    while (i < frase.size()) {
      frase[i] = tolower(frase[i]);
      vetor[int(frase[i]) - 97] = 1;
      i++;
    }
    i = 0;
    while (i < 26) {
      if (vetor[i] == 0) {
        cout << "NO\n";
        flag = 0;
        break;
      }
      i++;
    }
    if (flag == 1) cout << "YES\n";
  }
  return 0;
}
