#include<stdio.h>
#include<string.h>

int main () 
{
  int a,b,c,d;
  
  scanf("%d %d %d %d",&a,&b,&c,&d);

  while (1)
  {
  	c=c-b;
  	if ( c<=0 )
    {
    	printf("Yes");
    	return 0;
    }
    
    a=a-d;
    if ( a<=0 )
    {
    	printf("No");
      	return 0;
    }
        
  }

}