#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
int main() {
	long long h, w, n, k;
	cin >> h >> w >> n >> k;
	long long ans = h + w - 2;
	if (ans % n == k - 1) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}