#include<stdio.h>
int main(void){
  int ts,tp,as,ap,k,l;
  scanf("%d %d %d %d",ts,tp,as,ap);
  k=(ts-ts%ap)/ap;
  l=(as-as%tp)/tp;
    if(k>l){puts("Yes");}
  else if(k==l){puts(as%tp?"Yes":"No");}
  else{puts("No");}
 return 0; 
}