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 ??