(define (main args)
  (let*
    (
      (a (read))
      (b (read))
      (c (read))
      (d (read))
    )
    (let loop
      ((n 0))
      (if (equal? (modulo (+ (* a n) c) b) d)
        (print (+ c (* a n)))
        (loop (+ n 1)))))
  0)