#include <stdio.h>

int main(void){
	int c;
	double h, w, n, k;

	scanf("%lf %lf %lf %lf", &h, &w, &n, &k);
	c = (int)(h + w - 1) % (int)n;
	if(c == k)
		printf("YES\n");
	else if(c == 0){
		if(n == k)
			printf("YES\n");
		else
			printf("NO\n");
	}
	else
		printf("NO\n");
	return 0;
}