#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i = 0; i < n; i++)
#define rrep(i,n) for (int i = n-1; i >= 0; i--)
#define rep2(i,a,b) for (int i = a; i < b; i++)
#define rrep2(i,a,b) for (int i = a-1; i >= b; i--)
#define rep3(i,a,b,c) for (int i = a; i < b; i+=c)
#define rrep3(i,a,b,c) for (int i = a-1; i >= b; i-=c)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
template<class T> bool chmax(T &a, T b){if (a < b){a = b;return true;} else return false;}
template<class T> bool chmin(T &a, T b){if (a > b){a = b;return true;} else return false;}

int n;
string s;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>n>>s;
    int ans=n-1,t=0;;
    rep(i,n-2){
        if(s[i]=='B'&&s[i+1]=='A'&&s[i+2]=='B')ans--;
    }
    rep(i,n-1){
        if(s[i]=='B'&&s[i+1]=='B'){
            ans--;
            t=1;
        }
    }
    ans+=t;
    cout<<ans<<"\n";
}