#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;

int main()
{
    ll n, cnt1 = 0, scnt = 0;
    bool on = false;
    string s, tmp;
    cin >> n >> s;
    for (int i = 0; i < n-1; i++){
        if (s[i] == 'B') on = true;
        if (s[i] == 'A' && s[i+1] == 'A' && on){
            if (on && cnt1 >= 2) scnt += (cnt1 - 2);
            cnt1 = 0;
            on = false;
        }
        if (on) cnt1++;
        if (i == (n-2) && on){
            if (s[i+1] == 'B'){
                cnt1++;
                scnt += (cnt1 -2);
            } else scnt += (cnt1 - 2);
        }
    }
    cout << s.size() - 1 - scnt << endl;
}