#define_CRT_SECURE_NO_WARNINGS

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