#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <limits.h>
#include <algorithm>
#include <math.h>
#include <array>

using namespace std;
using ll = long long;

signed main()
{
	iostream::sync_with_stdio(0);
	cin.tie(0);

	int n;
	string str;
	cin >> n >> str;

	vector<int> left(n), right(n);
	left[0] = str[0] == 'A';
	for (int i = 1; i < n; i++) left[i] = left[i - 1] + (str[i] == 'A');
	right[n - 1] = str[n - 1] == 'K';
	for (int i = n-2; 0 <= i; i--) right[i] = right[i + 1] + (str[i] == 'K');

	int best = 0;
	for (int i = 0; i < n-1; i++) best = max(best, min(left[i], right[i + 1]));
	cout << best*2;
}