import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T read(T)(){ return read.to!T; }
T[] read(T)(long n){ return n.iota.map!(_ => read!T).array; }
T[][] read(T)(long m, long n){ return m.iota.map!(_ => read!T(n)).array; }
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	
	int n = read!int;
	string s = read!string;
	
	int best = 100_000;
	foreach(int i; 0 .. n - 3){
		string q = s[i .. i + 4];
		int x = diff(q[0], 'A') + diff(q[1], 'C') + diff(q[2], 'T') + diff(q[3], 'G');
		if(x < best) best = x;
	}
	
	best.writeln;
	
}

int diff(char a, char b){
	int res;
	if(a > b) res = min(a - b, b + 26 - a);
	else res = min(b - a, a + 26 - b);
	return res;
}
