#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <cmath>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define fi first
#define se second

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