#include<stdio.h>

int main(void)
{
  int a,b,c,d;
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  scanf("%d",&d);
  while(-1){
  c=c-b;
    if(c<=0){
    printf("Yes");break;
    }
   a=a-d;
    if(a<=0){
    printf("No");break;
    }
  }
 return 0;
}