#include <iostream>
#include <string>
using namespace std;
int main()
{
string str;
char alphabetSmall[26] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };
char result[26]{};
int n;
int flag = 0;
cin >> n;
cin >> str;
for (int i = 0; i < n; i++)
{
for (int j = 0; j < 26; j++)
{
if (alphabetSmall[j] == str[i] || (alphabetSmall[j] - 32) == str[i])
{
result[j] = str[i];
break;
}
}
}
for (int i = 0; i < 26; i++)
{
if (result[i] == 0)
{
cout << "NO" << endl;
flag = 1;
break;
}
}
if (flag == 0) cout << "YES" << endl;
}