#!/usr/bin/env python3
#coding:utf-8

import math
import string
import random
from sys import stdin
# import numpy as np
# from matplotlib import pyplot as plt
	

def main():
	read=stdin.readline

	#edit here!
	h,w,n,k=map(int,read().split())
	if (h+w-1)%n==k:
		print("YES")
	else:
		print("NO")


if __name__ == '__main__':
	main()