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

using ll = long long;
#define all(a) begin(a), end(a)
#define sz(x) (int)((x).size())

#ifdef LOCAL
#include "debug.hpp"
#else
#define debug(...) 42
#endif

void solve() {
  string s; cin >> s;
  assert(s.length() <= 2e5);
  vector<int> p;
  for (int i = 0; i < sz(s); i++) {
    assert(s[i] == 'A' || s[i] == 'B');
    if (s[i] == 'A') p.emplace_back(i);
  }
  ll ans = 0;
  for (int i = 0; i < sz(p); i++) ans += p[i] - i;
  cout << ans << '\n';
}

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);

  int T = 1;
  // cin >> T;
  while (T--) solve();

  return 0;
}