#include <stdio.h>

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