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