#include<stdio.h>

int main()
{
	int A,B,C,D;
	while(scanf("%d %d %d %d",&A,&B,&C,&D)!=EOF)
	while(A>0 && B>0)
	{
		C=C-B;
		if(C<=0)
		{
			printf("Yes\n");
			break;
		}
		A=A-D;
		if(A<=0)
		{
			printf("No\n");
			break;
		} 
	}	
	return 0;
 } 