package main

import (
	"fmt"
)

func main() {
	var n, m, x, y int
	fmt.Scan(&n, &m, &x, &y)
	x -= 1
	y -= 1
	if  x/m%2 == y/m%2{
		if x%m == y%m{
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}else {
		if x%m == abs(m-1-(y%m)){
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

func abs(i int) int{
	if i<0 {
		return i*(-1)
	}
	return i
}