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