#include<stdio.h>
#include<math.h>
main()
{
    long long int a,b,c,d,e,f;
    scanf("%lld%lld%lld%lld",&a,&b,&c,&d);
    while(1)
    {
        c=c-b;
        if(c<=0)
        {
            printf("Yes");
            break;
        }
        a=a-d;
        if(a<=0)
        {
            printf("No");
            break;
        }
    }
  
 
}