#include<stdio.h>
#include<math.h>
int main()
{
    long long a,b,c,d,m,n,s1,s2;
    scanf("%lld%lld%lld%lld",&a,&b,&c,&d);
    m=(floor)((float)c/b);
    n=(floor)((float)a/d);
    s1=c-(b*m);
    s2=a-(d*n);
    if(s1<=s2)
        printf("Yes\n");
    else
        printf("No\n");
    return 0;
}