#include<stdio.h>
int main()
{int a,b,c,d,e,f;
 scanf("%d %d %d %d",&a,&b,&c,&d);
 
 if(a%d==0) e=a/d;
 else e=a/d+1;
 
  if(c%b==0) f=c/b;
 else f=c/b+1;
 
 if(f<=e) printf("Yes");
 else printf("No");
return 0;
}