#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(void){
  string s;
  cin >> s;
  int ans = 0;
  int c = 0;
  for(int i = 0; i < s.length(); i++){
    if(s[i] == 'A') ans += c;
    else c++;
  }
  cout << ans << endl;
  return 0;
}