#include <iostream>
#include <vector>
#include <sstream>
using namespace std;


int main()
{
	string in;
	int temp;
	vector<int> v;

	getline(cin,in);
	stringstream ss(in);
	
	while(!ss.eof()){
		ss>>temp;
		v.push_back(temp);
		ss.ignore();
	}

	int h,w,n,k;
	h = v.at(0);
	w = v.at(1);
	n = v.at(2);
	k = v.at(3);
	if((h*w) % n == n - k){
		cout<<"YES"<<endl;
	}else{
		cout<<"NO"<<endl;
	}
	return 0;
}