// No.559 swapAB列
// https://yukicoder.me/problems/no/559
//
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
using namespace std;

vector<int> check_A_positions(string &S);


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

    vector<int> res = check_A_positions(S);
    int after_swap = (0 + res.size()-1) * res.size() / 2;
    int current_status = accumulate(res.begin(), res.end(), 0);
    cout << current_status - after_swap << endl;
}

vector<int> check_A_positions(string &S) {
    vector<int> res;
    for (auto i = 0; i < S.size(); ++i) {
        if (S[i] == 'A')
            res.push_back(i);
    }
    return res;
}