#include<stdio.h>
int main ()
{
  int A,B,C,D,i,a=0,b=0;
  scanf ("%d %d %d %d",&A,&B,&C,&D);
  if (A>=1&&A<=100&&B>=1&&B<=100&&C>=1&&C<=100&&D>=1&&D<=100)
  {
      for (i=1;i<=100;i++)
      {
          C=C-B;
          A=A-D;
      if (C<=0)
          {
              printf ("Yes\n");
              break;
          }
      if (A<=0)
         {
           printf ("No\n");
              break;
         }
      }
  }
  return 0;
}
