#include<bits/stdc++.h>
using namespace std;
long long t,h,w,n,k;
int main()
{
	t=1;
	while(t--)
	{
		cin>>h>>w>>n>>k;
		if((h+w-2)%n+1==k)cout<<"YES\n";
		else cout<<"NO\n";
	}
}