#include <cstdio>
#include <cstdlib>
#include <cstddef>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <iostream>
#include <iomanip>

int main(void)
{
	int h, w, n, k;
	std::cin >> h >> w >> n >> k;
    if((h + w - 1) % n == k % n){//h+w=5: 4ninme 2nara 2ninme
        std::cout << "YES" << std::endl;
    } else {
        std::cout << "NO" << std::endl;
    }
	return 0;
}