#include <iostream>

using namespace std;


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

    return 0;
}