#include<stdio.h>
int main(void)
{
int a,b,c,d;


scanf("%d",&a);
scanf("%d",&b);
scanf("%d",&c);
scanf("%d",&d);

while (a> 0 || c > 0)
{
c -= b;
if (c<= 0)
{
printf("Yes");
break;
}

a -= d;
if (a<= 0)
{
printf("No");
break;
}


return 0;}
