#include<stdio.h>
int main()
{
	long long int h, w, n, k;
	scanf("%lld %lld %lld %lld", &h, &w, &n, &k);
	if ((h + w - 2) % n == k - 1)
		printf("YES\n");
	else
		printf("NO\n");
	return 0;
}