#include<stdio.h>

int main(void)
{
   int a, b, c, d;

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

   if((c/b<a/d)||(((c/b-1)<=a/d)&&((c%b==0)||(a%d!=0))))
      printf("Yes\n");
   else
      printf("No\n");
   return 0;
}