#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>


using namespace std;


int main() {
	
	long long h, w, n, k;
	cin >> h >> w >> n >> k;
	if ((h + w - 2) % (n)+1 == k)cout << "YES" << endl;
	else cout << "NO" << endl;


	return 0;


}