#include<bits/stdc++.h>
#define int long long
#define PII pair< int, int >
using namespace std;
signed main()
{
		int h, w, n, k;
		cin >> h >> w >> n >> k;
		if((h+w-1)%n == k%n) cout << "YES\n";
		else cout << "NO\n";
	return 0;
}