#include <iostream>
#include <string>
using namespace std;
int main(int argc, char* argv[])
{
	string s;
	cin>>s;
	int i;
	int Na=0;
	int Nb=0;
	size_t sLen=s.length();
	for (i=0;i<sLen;i++){
		if (s[i]=='A'){
			Na++;
		}else{
			Nb++;
		}
	}
	size_t j=Na;
	size_t aw=0;
	for (i=0;i<sLen-Nb;i++){
		if (s[i]=='B'){
			for (;j<sLen;j++){
				if (s[j]=='A'){
					s[i]='A';
					s[j]='B';
					aw+=j-i;
					break;
				}
			}
		}
	}
	cout<<aw<<endl;
	return 0;
}