FLsiDublu

int FLsiDublu(Nod *head)
{
    int n=0;
    Nod *p=head;
    while(p!=NULL)
        ++n,p=p->leg;
    if(n%2)
        return -1;
    else
    {
        p=head;
        int m=n/2;
        Nod *q;
        while(m)
        {
            --m;
            if(m==0)
                q=p;
            p=p->leg;
        }
        int val=q->info;
        q=q->leg;
        m=n/2;
        bool ok=false;
        p=head;
        while(m--)
        {
            if(p->info!=q->info)
            {
                ok=true;
                break;
            }
            p=p->leg,q=q->leg;
        }
        if(ok)
            return -1;
        else
            return val;
    }
}