#include<bits/stdc++.h>
using namespace std; using ll=long long; using Pa=pair<ll,ll>; using Vll=vector<ll>; using VVll=vector<Vll>; using Vb=vector<bool>; using VVb=vector<vector<bool>>; using Vs=vector<string>; using VVs =vector<vector<string>>; using Vc=vector<char>; using VVc =vector<vector<char>>; const ll MOD=1000000007; const ll INF=(ll)1<<60;// 10^18 < 1<<60 = 1152921504606846976 // VVll G(N+1,Vll(0));   // vector<Pa> event; event.emplace_back(a,b); // 以下の関数 oi:エラー出力  OI:正出力  OIV:1次元vector正出力  OIVV:2次元vector正出力 
template<class t,class u> bool chmax(t&a,u b){if(a<b){a=b; return true;} else{return false;}}template<class t,class u> bool chmin(t&a,u b){if(b<a){a=b; return true;} else{return false;}} void oi(){}template<class Head, class... Tail>void oi(Head&& head,Tail&&... tail){if(sizeof...(tail)!=0){cerr<<head<<" ";} else{cerr<<head<<"\n";}oi(move(tail)...);} void OI(){}template<class Head, class... Tail>void OI(Head&& head,Tail&&... tail){if(sizeof...(tail)!=0){cout<<head<<" ";} else{cout<<head<<"\n";}OI(move(tail)...);} void OIV(){}template<typename T> void OIV(T &a){if(a.empty()){cout<<"\n"; return;} for(ll i00=0;i00<(a).size();i00++){if(a[i00]==(ll)1<<60){cout<<"I";} else{cout<<a[i00];} if(i00==(a).size()-1){cout<<"\n";} else{cout<<" ";}}} void OIVV(){}template<typename T> void OIVV(T &a){if(a.empty()){cout<<"\n"; return;} for(ll i00=0;i00<(a).size();i00++){for(ll j00=0;j00<(a[i00]).size();j00++){if(a[i00][j00]==(ll)1<<60){cout<<"I";} else{cout<<a[i00][j00];} if(j00==(a[i00]).size()-1){cout<<"\n";} else{cout<<" ";}}}}
#define FOR(i,a,b) for(ll i=(ll)(a); i<(ll)(b); i++)// a ~ b-1 i++ 
#define ALL(a) (a).begin(),(a).end()//   printf("%8.10lf\n",(ans));

int main(){// 解説読んで勉強
    ll N; cin>>N;
    string S; cin>>S;

    ll ans=N-1;// 普通にやるとN-1通りある
    FOR(i,0,N-2){// どちらもBBBになる
        if(S.substr(i,3)=="BAB") ans-=1;
    }
    ll bb=0;
    FOR(i,0,N-1){// 2個以上あると-1していく
        if(S.substr(i,2)=="BB") bb+=1;
    }
    if(bb>=2) OI(ans-(bb-1));// 
    else OI(ans);

    return 0;
}