#include<iostream>
#include<algorithm>
using ll = long long ;
using namespace std;
int main(){
	string str;
	ll ans=0;
	cin >> str;
	for(ll i=0;i<str.size();i++){
		ll count=0;
		for(ll j=i;j<str.size();j++){
			if(str[j]=='A')	count++;
			else	count--;
			if(count==0)	ans = max(ans,j-i+1);
		}
	}
	cout << ans << endl;
	return 0;
}