Re: ambiguous overload

#include<iostream>
using namespace std;
class Integer{
int i;
public:
Integer(int ii):i(ii){}
const Integer operator+(const Integer& rv){
cout<<"1-operator+"<<endl;
return Integer(i+rv.i);
}
Integer operator+=(Integer rv){
i+=rv.i;
cout<<"2-operator+="<<endl;
return *this;
}
friend Integer& operator+(Integer,Integer);

void display(){
cout<<"3-display()// i="<<i<<endl;
}};

Integer& operator+(Integer rv,Integer rs ){
cout<<"2-operator+="<<endl;
rv.i+=rs.i;
return rv;}

int main(void){
cout<<"buit-in types"<<endl;
int i=1,j=2,k=3;
k+=i+j;
cout<<"user defined types:"<<endl;
Integer ii(1),jj(2),kk(3);
kk+=ii+jj;
Integer d(1),b(2);
d=2+b;
d.display();
return 0;

}

g++ -g -Wall -o test test.cpp
test.cpp: In function 'Integer& operator+(Integer, Integer)':
test.cpp:22: warning: reference to local variable 'rv' returned
test.cpp: In function 'int main()':
test.cpp:33: error: ambiguous overload for 'operator+' in 'ii + jj'
test.cpp:7: note: candidates are: const Integer Integer::operator+
(const Integer&)
test.cpp:22: note: Integer& operator+(Integer,
Integer)
make: *** [test] Error 1
??

What should I do to prevent this ??