6 friend function

#include <iostream>
using namespace std;
class second;
class first{
    int x;
    public:
    void getvalue(){
        cout<<"Enter number ";
        cin>>x;
    }
    friend void sum(first,second);
};
class second{
    int y;
    public:
    void getvalue(){
        cout<<"Enter number ";
        cin>>y;
    }
    friend void sum(first,second);
};
void sum(first a , second b){
    cout<<"\nsum is "<<a.x+b.y;
}
int main()
{
    first a;
    second b;
    a.getvalue();
    b.getvalue();
    sum(a,b);
    return 0;
}
/*
Output
Enter number 1
Enter number 2

sum is 3
*/