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

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

int main() {
	int n; cin >> n;
    string s; cin >> s;
    vector<int> o(n , n+2);
    int a=0;
    for(int i = 0; i < n; i++){
        if(s[i]=='A')a++;
        o[i] = min(o[i] , a);
    }
    int b = 0;
    for(int i = n-1; i >= 0; i--){
        o[i] = min(o[i] , b);
        if(s[i]=='K')b++;
    }
    int ans = 0;
    for(int i = 0; i < n; i++)ans = max(ans , 2*o[i]);
    cout << ans << endl;
}