#include <stdio.h>
#include <stdbool.h>

int main(void) {
	int A, B, C, D;
	int Ta, Ao;
	
	scanf("%d %d %d %d", &A, &B, &C, &D);
	
	Ta = C/B;
	Ao = A/D;
	if(C%B != 0) Ta++;
	if(A%D != 0) Ao++;
	
	if(Ta <= Ao) {
		printf("Yes\n");
	} else {
		printf("No\n");
	}
	
	return 0;
}
