#include <iostream>
#include <algorithm>

using namespace std;

int main() {
	long long h, w, n, k;
	cin >> h >> w >> n >> k;
	long long minTurns = min(h, w);
	long long maxTurns = h + w - 1;
	if (maxTurns - minTurns >= n) {
		cout << "YES" << endl;
	} else if (maxTurns % n > minTurns % n) {
		cout << ((minTurns % n <= k % n && k % n <= maxTurns % n) ? "YES" : "NO") << endl;
	} else {
		cout << ((maxTurns % n <= k % n && k % n <= minTurns % n) ? "NO" : "YES") << endl;
	}
	return 0;
}