#include <bits/stdc++.h>
using namespace std;
bool isin(int s[], int n, int c) {
  for (int i = 0; i < n; i++) {
    if (s[i] == c) return true;
  }
  return false;
}
string lower(string s) {
  string result = "";
  for (int i = 0; i < s.size(); i++) {
    char c = s[i];
    if (int(s[i]) >= 97 and int(s[i]) <= 122)
      result += c;
    else
      result += char(int(c) + 32);
  }
  return result;
}
int main() {
  int n;
  cin >> n;
  string k;
  cin >> k;
  string s = lower(k);
  int chars[26] = {0};
  for (int i = 0; i < n; i++) {
    chars[int(s[i]) - 97]++;
  }
  if (!isin(chars, 26, 0)) {
    cout << "YES";
  } else {
    cout << "NO";
  }
}
