fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s = s.trim();

    let idx_sum_final: usize = (0..s.matches('A').count()).sum();
    let idx_sum_now: usize = s
        .char_indices()
        .filter(|&(_, c)| c == 'A')
        .map(|(i, _)| i)
        .sum();

    println!("{}", idx_sum_now - idx_sum_final);
}