#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
template<class T> inline bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T&a,T b){if(a>b){a=b;return 1;}return 0;}
using ll = long long;

int n;
string s;

int main () {
    ios::sync_with_stdio(false); 
    cin.tie(0); 

    cin >> n >> s;

    int ans=0, bb=0;
    rep(i,n-1) s.substr(i,2)!="BB" ? ans++ : bb=1;
    rep(i,n-2)if(s.substr(i,3)=="BAB") ans--;
    ans+=bb;    

    cout << ans << '\n';

    return 0;
}