
#include<stdio.h>
 
int main(){
  
  int A,B,C,D,a,b,c,d;
  int x,y;
  
  scanf("%d%d%d%d",&A,&B,&C,&D);
  
  a=A;
  b=B;
  c=C;
  d=D;
  
  x=a/d;
  y=c/b;
    
  
  puts(x>=y ? "No":"Yes");
  
  return 0;
  
}