#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cmath>
#include <stack>
#include <queue>
#include <cctype>
#include <stdio.h>
#include <map>
#include <string.h>
#include <utility>

typedef long long ll;
using namespace std;

typedef pair<int, int> P;

int main() {

	ll h,w,n,k;
	cin>>h>>w>>n>>k;


	if((w+h-1)%n ==0){
		if(n==k){
			cout<<"YES"<<endl;
			return 0;
		}
	}

	if((w+h-1)%n ==k){
		cout<<"YES"<<endl;
	}else {
		cout<<"NO"<<endl;
	}


	return 0;
}