#include <algorithm>
#include <cstdlib>
#include <iostream>
#include <vector>
#include <math.h>
using namespace std;
#define int long long

signed main() {
	string s;
	cin >> s;
	int res = 0;
	int st = 0;
	for (int i = 0; i < s.size(); i++) {
		if (s[i] == 'A') {
			res += i - st;
			st++;
		}
	}
	cout << res << endl;
	return 0;
}