package main

import "fmt"

func main() {
	var H, W, N, K int
	fmt.Scanf("%d %d %d %d", &H, &W, &N, &K)
	if ((H + W - 1 - 1) % N) + 1 == K {
		fmt.Println("YES")
	} else {
		fmt.Printf("NO")
	}

}