package main

import "fmt"

func class(M, x int) int {
	if x == 0 {
		return 1
	} else if x <= M {
		return x
	} else {
		return 2*M + 1 - x
	}
}
func main() {
	var N, M, X, Y int
	fmt.Scan(&N, &M, &X, &Y)

	x := class(M, X%(2*M))
	y := class(M, Y%(2*M))

	if x == y {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}