#include<stdio.h>
void main()
{
  int A,B,C,D;
  scanf("%d %d %d %d",&A,&B,&C,&D);
  while(C<=0 || A<=0)
  {
    C=C-B;
    if(C<=0)
      break;
    A=A-D;
  }
  if(C<=0)
    printf("Yes");
  else
    printf("No");
}
  
    
