#include <bits/stdc++.h>
using namespace std;
int main() {
  string a = "abcdefghijklmnopqrstuvwxyz";
  string b = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  int n, c = 0, k = 0, e = 0;
  string s;
  char d[10000];
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    s[i] = tolower(s[i]);
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < a.length(); j++) {
      if (s[i] == a[j] || s[i] == b[j]) {
        for (int v = e; v >= 0; v--) {
          if (d[v] == s[i]) k++;
        }
        if (k == 0) {
          c++;
          d[e] = s[i];
          e++;
          break;
        }
        c++;
        break;
      }
    }
    k = 0;
  }
  if (e == 26) {
    cout << "YES" << endl;
  } else {
    cout << "NO" << endl;
  }
  return 0;
}
