#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0; i < (int)(n); i++)
using namespace std;

int main(){
    string S;
    cin >> S;
    int count = 0, b = 0;
    for(auto s : S) {
        if(s == 'A') count += b;
        else ++b;
    }
    cout << count;
}