(define n (read))
(define m (read))
(define p (read))
(define q (read))
(define r (make-vector 12 1))
((rec (r-init i j)
  (unless (> i j)
          (begin 
            (set! (~ r (- i 1)) 2)
            (r-init (+ i 1) j)))) p (- (+ p q) 1))
(print ((rec (check rest a)
             (let1 rest1 
                   (- rest 
                      (* m 
                         (~ r (remainder a 12)))) 
                   (if (<= rest1 0)
                       (+ a 1)
                       (check rest1 (+ a 1)))))
        n 0))