#include<iostream>
using namespace std;
int main()
{
	//freopen("game.in","r",stdin);
	//freopen("game.out","w",stdout);
		int h,w,n,k;
		cin>>h>>w>>n>>k;
		int a=h-1+w;
		int ans=a%n;
		if(ans==k||ans==0&&k==n){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}
	return 0;
}