#include <bits/stdc++.h>
using namespace std;
int i, n, a[26];
string s;
int main() {
  cin >> n;
  cin >> s;
  if (n < 26) {
    cout << "NO" << endl;
    return 0;
  }
  for (i = 0; i < s.size(); i++) {
    if (s[i] < 'a')
      a[s[i] - 'A'] = 1;
    else
      a[s[i] - 'a'] = 1;
  }
  for (i = 0; i < 26; i++)
    if (a[i] == 0) {
      cout << "NO" << endl;
      return 0;
    }
  cout << "YES" << endl;
}
