(define yuki512
  (let*(
    (x (read))
    (y (read))
    (n (read))
    (_ (read-line))
    (a (map string->number (string-split (read-line) #\space)))
    (flag #t))
    (do
      ((i 0 (+ i 1)))
      ((= i (- n 1)))
      (when (> (* y (~ a i)) (* x (~ a (+ i 1)))) (set! flag #f)))
    (display (if flag "YES\n" "NO\n"))))