package main

import "fmt"

func main() {
	var x, y, xp, yp, a float64
	var n int
	_, _ = fmt.Scan(&x, &y, &n)
	x, y = 1, y/x

	c := make([]float64, n)
	for i := range c {
		_, _ = fmt.Scan(&a)
		c[i] = a
	}

	for i := 0; i < n-1; i++ {
		a = c[i]
		xp, yp = a, yp+(a-xp)*y
		if yp > c[i+1] {
			fmt.Println("NO")
			return
		}
	}
	fmt.Println("YES")
}