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