// Source: https://usaco.guide/general/io

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

int main() {
	int n,a=0,k=0;
    char b;
    cin>>n;
    for(int i=0;i<n/2;i++){
        cin>>b;
        if(b=='A'){
            a++;
        }
    }
    for(int i=0;i<n/2;i++){
        cin>>b;
        if(b=='K'){
            k++;
        }
    }
    cout<<min(a,k)*2;
}