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

typedef long long ll;

#define rep(i,a,b) for(int i=a; i<b; i++)
#define all(x) (x).begin(), (x).end()

template<class T>bool chmax(T& a, const T& b) { if(a<b) {a=b; return 1;} return 0;}
template<class T>bool chmin(T& a, const T& b) { if(b<a) {a=b; return 1;} return 0;}

using pii = pair<int, int>;
using pll = pair<ll, ll>;

const ll MOD = 1000000007;
const ll INF = 1LL << 60;

int main(){
	int N; string S; cin >> N >> S;
	int Ans=N-1;
	int cnt=0;
	rep(i,0,N-1){
		if(i<N-2 && S.substr(i,3)=="BAB") Ans--;
		if(S.substr(i,2)=="BB") cnt++;
	}
	if(cnt>0) Ans-=(cnt-1);
	cout << Ans << endl;

}