#include <bits/stdc++.h>
int main() {
  int x, type[26] = {0}, m = 0;
  char c;
  scanf("%d", &x);
  getchar();
  for (int i = 0; i < x; i++) {
    scanf("%c", &c);
    if (c <= 'Z') {
      type[c - 'A']++;
    } else {
      type[c - 'a']++;
    }
  }
  for (int i = 0; i < 26; i++) {
    if (type[i] == 0) {
      m++;
      break;
    }
  }
  if (m == 0) {
    printf("YES");
  } else {
    printf("NO");
  }
}
