#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s;
  map<char, int> p;
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    if (isupper(s[i])) {
      s[i] = tolower(s[i]);
    }
    p[s[i]]++;
  }
  for (char i = 'a'; i <= 'z'; i++) {
    if (p[i] == 0) {
      cout << "NO";
      return 0;
    }
  }
  cout << "YES";
  return 0;
}
