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

int main() {
	int n, suma=0; string s; cin>>n>>s;
	int a=0, b=n-1;
	while(a<b){
		while(s[a]!='A')
		a++;
		while(s[b]!='K')
		b--;
		if(!(a<b)){
			break;
		}
		suma++;
		a++;
		b--;
	}
	cout<<2*suma;
}