#include<stdio.h>

int main(void) {
	int a, b, c, d,t,s;
	scanf("%d%d%d%d", &a, &b, &c, &d);
	if (c % b == 0) t = c / b;
	else t = c / b + 1;
	if (a % d == 0) s = a / d;
	else s = a / d + 1;
	if (t<=s) printf("Yes");
	else printf("No");

	return 0;
}