#include<iostream>

using namespace std;

int main(){

	long long H, W, N, K;
	cin>> H>> W>> N>> K;

	if((max(H, W)-(N-(min(H, W)+N-1)%N)%N-K+N)%N==0) cout<< "YES"<< endl;
	else cout<< "NO"<< endl;

	return 0;
}