#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i=0;i<(int)(n);i++)

int main(){
  int n;
  cin>>n;
  string s;
  cin>>s;
  ll ans=0;
  int flg=0;
  rep(i,n-1){
    if(s.at(i)=='B'){
      if(s.at(i)==s.at(i+1)) flg=1;
      else if(i+2<n&&s.at(i+2)=='B');
      else ans++;
    }else ans++;
  }
  cout<<ans+flg<<endl;
}