/*---------------------------*\
____________Mari000____________
________Mostafa Shehab________
\*---------------------------*/
#include <bits/stdc++.h>
using namespace std;
#define PI 3.14159265
#define EPS (1e-10)
#define endl "\n"
typedef long long ll;
typedef long double ld;
ll power(ll x,ll y,ll p);
int Bit(ll x);
ll sum(ll x);
void Fast(){
std::ios_base::sync_with_stdio(0);
cin.tie(NULL); cout.tie(NULL);
}
inline int D(){
int t;
scanf("%d",&t);
return t;
}
inline ll llD(){
ll t;
scanf("%lld",&t);
return t;
}
const int N=55;
char arr[N];
bool visit[N];
int ans[N];
ll t,a,b,k;
void seive(){
for(int i=2;i<N;++i){
if(visit[i])
continue;
for(int j=i;j<N;j+=i)
++ans[j],visit[j]=true;
}
}
int mn=INT_MAX;
int main(){
int n=D();
scanf("%s",arr);
string str="ACTG";
for(int i=0;i<n-3;++i){
int count=0;
count+=min(abs(arr[i]-str[0]),abs('Z'-arr[i]+str[0]-'A'+1));
count+=min(abs(arr[i+1]-str[1]),abs('Z'-arr[i+1]+str[1]-'A'+1));
count+=min(abs(arr[i+2]-str[2]),abs('Z'-arr[i+2]+str[2]-'A'+1));
count+=min(abs(arr[i+3]-str[3]),abs('Z'-arr[i+3]+str[3]-'A'+1));
mn=min(count,mn);
}
cout<<mn;
}
ll power(ll x,ll y,ll p){
ll res = 1; // Initialize result
x = x % p; // Update x if it is more than or
// equal to p
while (y > 0){
// If y is odd, multiply x with result
if (y & 1)
res = (res*x) % p;
// y must be even now
y = y>>1; // y = y/2
x = (x*x) % p;
}
return res;
}
int Bit(ll x){
if(!x)
return 0;
return 1+Bit(x>>1);
}
ll sum(ll x){
return x*(x+1)/2;
}
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