#include<iostream> 

int main() {
	long long h, w, n, k;

	std::cin >> h >> w >> n >> k;

	// この回数番目の人は確実に負け
	long long lose = (h - 1) + w;

	if (lose % n == k || (n == k && lose % n == 0)) {
		std::cout << "YES" << std::endl;
	} else {
		std::cout << "NO" << std::endl;
	}

	return 0;
}