import java.util.Scanner
fun f(): Boolean {
    val sc = Scanner(System.`in`)
    val x = sc.nextInt()
    val y = sc.nextInt()
    val n = sc.nextInt()
    var a = sc.nextInt()
    for (i in 2..n) { val b=sc.nextInt(); if (a*y>b*x) return false; a=b }
    return true
}
fun main(args : Array<String>) {
    println(if (f()) "YES" else "NO")
}