package main

import . "fmt"

func main() {
	var x,y,n int
	Scan(&x,&y,&n)
	a := make([]int, n)
	for i:=range a {
		Scan(&a[i])
		if i>0{
			if a[i-1]*y > a[i]*x {
				Println("NO")
				return
			}
		}
	}
	Println("YES")
}