#include<iostream>
#include<sstream>
using namespace std;
int main()
{
int n,m=0;
char h='a';
cin>>n;
char s[n];
for(int l=0;l<n;l++){
cin>>s[l];
}
for(int j=0;j<n;j++){
if(!(isalpha(s[j]))){
cout<<"NO";
return 0;}
}
for(int i=0;i<n;i++){
if((int)s[i]<93)
s[i]=(int)s[i]+32;
}
for(int k=0;k<n;k++){
if(s[k]==h){
m++;
h++;
k=0;}
}
if(m>=26)
cout<<"YES";
else
cout<<"NO";
}
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