#include <bits/stdc++.h>
using namespace std;

int main() {

  string S;
  int cnt;
  int a_cnt;
  cin >> S;
  int n = S.length();

  cnt = 0;
  a_cnt = 0;

  for(int i = 0; i < n; i++){
    if(S[i] == 'A'){
      cnt += i - a_cnt;
      a_cnt++;
    }
  }

  cout << cnt << endl;

  return 0;

}