#include <stdio.h>
void main(){
  int a,b,c,d;
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  scanf("%d",&d);
  while(a>0){
    c=c-b;
    if(c<=0)
      break;
    a=a-d;
  }
  if(c<=0)
    printf("Yes\n");
  else
    printf("No\n");
  
}