(define (main args)
  (let* ([ls (string->list (read-line))])
    (print
     (let loop ([l ls]
                [i 0]
                [ia 0]
                [c 0])
       (cond [(null? l) c]
             [(char=? #\A (car l)) (loop (cdr l) (+ i 1) (+ ia 1) (+ c (- i ia)))]
             [else (loop (cdr l) (+ i 1) ia c)]))))
  0)