#include<stdio.h>
main()
{
	int a,b,c,d;
	scanf("%d %d %d %d",&a,&b,&c,&d);
	while(1)
	{
		c=c-b;
		if(c<=0)
		{
			printf("Yes");
			break;
		}
		a=a-d;
		if(a<=0)
		{
			printf("No");
			break;
		}
	}
}