#include<bits/stdc++.h>
using namespace std;

int main()
{
   int n,sum=0;
   int x[50];

    string s;

    cin>>n>>s;

    for(int i = 0; i<n-3;i++){
        x[i]= 0;

        x[i]+=min(abs(s[i]-'A'),(abs('Z'-s[i]+1)));
        x[i]+=min(abs(s[i+1]-'C'),(abs('Z'-s[i+1])+3));
       x[i]+=min(abs(s[i+2]-'T'),(abs('Z'-s[i+2])+20));
      x[i]+=min(abs(s[i+3]-'G'),(abs('Z'-s[i+3])+7));
if(x[i]<x[i-1])
{
    sum=x[i];
}
    }

    cout<<sum<<endl;

}