#include <bits/stdc++.h>
int main() {
  int n, i,
      a[26] =
          {
              0,
          },
      sum = 0;
  scanf("%d", &n);
  char word[n + 1];
  scanf("%s", word);
  for (i = 0; i < n; i++) {
    if (word[i] >= 'A' && word[i] <= 'Z') {
      word[i] += 'a' - 'A';
    }
    a[word[i] - 'a'] = 1;
  }
  for (i = 0; i < 26; i++) sum += a[i];
  if (sum == 26)
    printf("YES");
  else
    printf("NO");
  return 0;
}
