#include <bits/stdc++.h>

using namespace std;
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define rrep(i,n) for(int i=n-1;i>=0;--i)
#define debug(output) if(debugFlag)cout<<#output<<"= "<<output<<"\n";
using lint = long long;
typedef pair<int,int> P;
const bool debugFlag=true;
const lint linf=1.1e18;const int inf=1.01e9;
constexpr int MOD=1000000007;
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(a > b){ a = b; return 1; } return 0; }

template<class T>
vector<pair<T,int>> RunLengthPress(vector<T> a){
  int cnt=1;T last=a[0];
  int n=a.size();
  vector<pair<T,int>> res;
  rep1(i,n-1){
    if(last==a[i])++cnt;
    else{
      res.push_back({last,cnt});
      last=a[i];cnt=1;
    }
  }
  res.push_back({last,cnt});
  return res;
}

signed main(){
    int n;cin>>n;
    string s;cin>>s;
    vector<char> a(n);
    rep(i,n)a[i]=s[i];
    auto b=RunLengthPress(a);
    int res=0;
    if(b.size()==1){
        if(b[0].first=='B'){
            cout<<1<<"\n";
            return 0;
        }
        cout<<b[0].second-1<<"\n";
        return 0;
    }
    for(auto& [c,m]:b){
        if(c=='B')continue;
        if(m==1)++res;
        else res+=m+1;
    }
    for(auto& [c,m]:b){
        if(c=='B'&&m>=2){
            ++res;
            break;
        }
    }
    if(s[0]=='A'&&s[1]=='A')--res;
    if(s[n-2]=='A'&&s[n-1]=='A')--res;
    cout<<res<<"\n";
    return 0;
}