Calling ostream friend function of base class in c++

Question

So, I have two classes:

class Base {
    private:
        int number;
    public:
        friend ostream & operator<<(ostream & output, const Base &n);
}

ostream & operator<<(ostream & output, const Base &n) {
    output<<n.a<<endl;
    return output;
}

class Child : Base {
    private:
        int second;
    public:
        friend ostream & operator<<(ostream & output, const Child &n);

}

ostream & output<<(ostream & output, const Child &n) {
    output<<n.second<<Base:: ????<<endl;
    return output;
}

My question is, how can i call the friend function of the base class from the child class to output its content:

output<<n.second<<Base:: ????<<endl

Thanks in advance :)

Answer 1

output<<n.second<<static_cast<const Base&>(n)<<endl;