#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string str;
  cin >> n >> str;
  unordered_map<char, int> mp;
  for (auto& a : str) mp[::tolower(a)]++;
  if (mp.size() == 26)
    cout << "YES";
  else
    cout << "NO";
}
