#include<stdio.h>
 
int main(void){
  
  int ht,at,ha,aa;
  
  scanf("%d",&ht);
  scanf("%d",&at);
  scanf("%d",&ha);  
  scanf("%d",&aa);
   
  while(1){
     ha=ha-at;
       if(ha<=0){
         puts("Yes");
         break;}
     
     
     ht=ht-aa;
       if(ht<=0){
         puts("No");
         break;}
   }
 
  
  return 0;
}