#define _GLIBCXX_DEBUG
#import <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, n) for (int i = 1; i < (int)(n); i++)
typedef long long ll;

int main() { 
 int a;string s;cin>>a>>s;int res = a-1;int base = 0;
 rep(i,a-1){
     if(s[i]=='B'&&s[i+1]=='B'){res--;base = 1;}
 }
 rep(i,a-2){
     if(s[i]=='B'&&s[i+1]=='A'&&s[i+2]=='B'){res--;}
 }
 cout << res+base << endl;
}