#include <bits/stdc++.h>
using namespace std;
int main() {
  int a = 0, b;
  string s = "qwertyuiopasdfghjklzxcvbnm";
  string f = "QWERTYUIOPASDFGHJKLZXCVBNM";
  string n;
  cin >> b;
  cin >> n;
  for (int j = 0; j < n.size(); j++) {
    for (int i = 0; i < 26; i++) {
      if (n[j] == s[i] or n[j] == f[i]) {
        a++;
        s[i] = '0';
        f[i] = '0';
      }
    }
  }
  if (a == 26)
    cout << "YES";
  else
    cout << "NO";
}
