#include <bits/stdc++.h>
using namespace std;
int main() {
	string S;
	cin >> S;
	int ans = 0;
	int count = 0;
	for(int i = 0; i < S.length(); i++) {
		if(S[i] == 'A') ans += count;
		else count++;
	}
	cout << ans << endl;
	return 0;
}