#include<stdio.h>

int main(void){
  
  int ht,ha,at,aa;
  
  scanf("%d %d %d %d",&ht,&ha,&at,&aa);
 
   while(1){
     ha=ha-at;
       if(ha<=0){
         printf("Yes");
         break;}
     
     ht=ht-aa;
       if(ht<=0){
         printf("No");
         break;}
   }

  return 0;
}