#include <stdio.h>
int main(){
  int thp,tatk,ahp,aatk;
  scanf("%d%d%d%d",&thp,&tatk,&ahp,&aatk);
    do{
     ahp-=tatk;
     thp-=aatk;
    }while(thp>0&&ahp>0);
  if(ahp<=0&&thp>0)
    printf("Yes");
  else if(ahp<=0&&thp<=0)
    printf("Yes");
  else printf("No");
  return 0;
}