#include<stdio.h>
main()
{
    int A,B,C,D,e,f,c=0,c1=0;
    scanf("%d%d%d%d",&A,&B,&C,&D);
    while(1)
    {
        e=A-D;
        c++;
        A=e;
        if(e<=0)
            break;
    }
    while(1)
    {
        f=C-B;
        c1++;
        C=f;
        if(f<=0)
            break;
    }
    if(c<c1)
        printf("No\n");
    else
        printf("Yes\n");
}
