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