#include <stdio.h>

int main(){
 int a;
 int b;
 int c;
 int d;
  
 scanf("%d %d %d %d",&a,&b,&c,&d);


 do{   
  c = c - b;
  a = a - d;   
 } while((a > 0) || (c > 0));
   

  a = a + d; 
  c = c + b;      

 if(c - b >= 0){
  printf("Yes"); 
 }else{
  printf("No"); 
 }
  
  
 return 0;
}