#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

//#include<bits/stdc++.h>



int main() {
	
	string s;
	cin >> s;

	int ans = 0;
	int c = 0,d=0;
	for (int i = 0; i < s.size(); i++) {
		if (s[i] == 'A')ans+=c;
		else c++;
	}

	
	
	cout << ans << endl;

	return 0;
}