#include <cstdio>
#include <string>
#include <iostream>
using namespace std;
int main(){
	string s;
	getline(cin, s);
	int countB = 0;
	int ans = 0;
	int size = s.size();
	for(int i = 0; i < size; i++){
		if(s[i] == 'A'){
			ans += countB;
		}else{
			countB++;
		}
	}
	printf("%d\n", ans);
	return 0;
}