#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
using namespace std;

int main(void){
	long long  h, w, n, k;
	cin >> h >> w >> n >> k;
	long long sum = h + w - 1;
	long amari = sum % n;
	//modで計算
	if(amari == (k % n)) printf("YES\n");
	else printf("NO\n");
	return 0;
}