#include <bits/stdc++.h>
using namespace std;
int main() {
  int l;
  cin >> l;
  string s;
  cin >> s;
  if (l < 26) {
    cout << "NO\n";
    return 0;
  }
  int f[26] = {};
  for (int i = 0; i < l; i++) f[tolower(s[i]) - 'a']++;
  for (int i = 0; i < 26; i++)
    if (f[i] == 0) {
      cout << "NO\n";
      return 0;
    }
  cout << "YES\n";
  return 0;
}
