#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

string S;

int main() {
  cin >> S;
  int N = S.size();
  int ans = 0, le = 0;
  for (int i = 0; i < N; i++) {
    if (S[i] == 'A') {
      ans += i - le;
      le++;
    }
  }
  cout << ans << endl;
  return 0;
}