#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    cin >> n;

    string s;
    cin >> s;

    vector<int> van(n + 1);
    for(int i = n - 1; i >= 0; i--){
        van[i] = van[i + 1];
        if(s[i] == 'K'){
            van[i]++;
        }
    }

    int alma = 0;
    int ans = 0;

    for(int i = 0; i < n; i++){
        if(s[i] == 'A'){
            alma++;
        }

        ans = max(ans, 2*min(alma, van[i + 1]));
    }

    cout << ans << "\n";
}