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