#include <bits/stdc++.h>
using namespace std;
const int maxn = 6e5 + 10;
using namespace std;
int h[200];
int main() {
  int n;
  string s;
  bool re = true;
  cin >> n;
  cin >> s;
  for (int i = 0; i < s.length(); ++i) {
    h[s[i]]++;
  }
  for (int i = 'a'; i <= 'z'; ++i) {
    if (h[i] == 0 && h[i - 32] == 0) re = false;
  }
  if (re)
    puts("YES");
  else
    puts("NO");
  return 0;
}
