#include <bits/stdc++.h>
using namespace std;
int freq[27];
char sent[101];
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", sent);
  while (n--) {
    if (isupper(sent[n])) sent[n] = tolower(sent[n]);
    freq[sent[n] - 'a']++;
  }
  for (int i = 0; i < 26; i++)
    if (!freq[i]) {
      printf("NO\n");
      return 0;
    }
  printf("YES\n");
  return 0;
}
