#include <iostream>
#include <cstdio>

using namespace std;

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