#include <iostream>
#include <string>

using namespace std;

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

    int len = ab.length();
    int aCount = 0;
    int result = 0;

    for (int i = 0; i < len; i++) {
        if (ab[i] == 'A') {
            result += i - aCount++;
        }
    }

    cout << result << "\n";

    int a;
    cin >> a;
}