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

signed main(){
    ios::sync_with_stdio(false);cin.tie(nullptr);
    int n; cin >> n;
    string s; cin >> s;
    vector<int>a(n), b(n);
    for(int i = 0; i < n; i++)
    {
        if(s[i] == 'A') a[i] = 1;
        if(i > 0) a[i] += a[i-1];
    }
    int ans = 0;
    for(int i = n-1; i >= 0; i--)
    {
        if(s[i] == 'K') b[i] = 1;
        if(i < n-1) b[i] += b[i+1];
        ans = max(ans, min(b[i], a[i]) * 2);
    }
    cout << ans;
}