#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string str;
  cin >> str;
  int count = 0;
  for (int i = 0; i < n; i++) {
    if (str[i] >= 'A' && str[i] <= 'Z') str[i] = str[i] + 32;
  }
  sort(str.begin(), str.end());
  for (int i = 0; i < n; i++) {
    if (str[i] == str[i + 1]) count++;
  }
  if (n - count == 26)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
