#include <iostream>

using namespace std;

char str[100002];

int main()
{
    int N;
    cin >> N >> str;
    int count_A = 0, count_K = N/2;
    int result = 0;
    for(int i = 0; str[i] != '\0'; i++){
        if(str[i] == 'K'){
            count_K--;
        }
        else{
            count_A++;
        }
        if(result < 2*min(count_A, count_K)){
            result = 2*min(count_A, count_K);
        }
    }
    cout << result;
    return 0;
}