#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  set<char> letters;
  for (int i = 0; i < n; i++) {
    if (s[i] >= 65 && s[i] <= 90) s[i] = s[i] + 32;
  }
  for (int i = 0; i < n; i++) {
    letters.insert(s[i]);
  }
  if (letters.size() == 26)
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
