重載运算符问题，为啥有歧义

#include <iostream>
using namespace std;
class Point
{
public:
    Point(int a,int b);
    friend ostream & operator<<(ostream &output,Point &p );
    void getxy();
public:
    int  x,y;
};
Point::Point(int a,int b)
    {
        x=a;
        y=b;
    }
void Point::getxy()
{
    cout<<"input x,y:"<<endl;
    cin>>x>>y;
}
class Circle:public Point
{
public:
    friend ostream & operator<<(ostream &output,Point &p );
    Circle(int a,int b,int r1);
    int area();
    void getr();
    int r;
};
Circle::Circle(int a,int b,int r1):Point(a,b),r(r1){}
void Circle::getr()
{
    cout<<"inpu r:"<<endl;
    cin>>r;
}
int Circle::area()
{
    return 3.14*r*r;
}
class Cyinder:public Circle
{
public:
    int h;
};
ostream & operator<<(ostream &output,Circle &C )
{
    output<<C.x<<endl<<C.y<<endl<<C.area()<<endl;
    return output;
}
ostream & operator<<(ostream &output,Point &p )
{
    output<<p.x<<endl<<p.y<<endl;
    return output;
}
int main()
{
    Point o(1,2);
    o.getxy();
    cout<<o;
    Circle c(1,2,3);
    c.getr();
    cout<<c;
    return 0;                  
}