#include<stdio.h>
int main(void){
  int a,b,c,d;
  
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  scanf("%d",&d);
  
  if(a/d>c/b){
    printf("No");
}else{
  printf("Yes");
 }
  return 0;
}