#include<stdio.h>
int main(void) {
	int a, b, c, d,e,f;
	scanf("%d", &a);
	scanf("%d", &b);
	scanf("%d", &c);
	scanf("%d", &d);

	if (c % b == 0) e = c / b;
	else  e = c / a + 1;
	if (a % d == 0) e = a / d;
	else  f = a / d + 1;

	if (e <= f)printf("Yes");
	else printf("No");
	return 0;


}