#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==1) {puts(as%tp==0?"No":"Yes");}
  else{puts("No");}
 return 0; 
}
