#!/usr/bin/env perl

use strict;
use warnings;

my $in = <>; chomp $in;
my @vs = (split //,$in);
my $countA = 0;
my $res = 0;
while (my ($index, $c) = each(@vs)) {
  if ($c eq 'A') {
    $res += $index - $countA;
    $countA++;
  }
}
print $res . "\n";