#include<stdio.h>


int main(){
  int A,B,C,D,taka,ao;
  scanf("%d%d%d%d",&A,&B,&C,&D);
  taka=A/D;
  ao=C/B;
  if(A%D!=0)taka++;
  if(C%B!=0)ao++;
  if(taka<ao)printf("No");
  else printf("Yes");
};
   