#include <iostream>
using std::cout;
using std::endl;

#include <string>
using std::string;

struct String
{
    string  s;

    String( string str ) : s( str )
    {
    }

    String operator+( const String &rhs ) const
    {
        String  tmp( s );

        tmp.s.append( rhs.s );

        return tmp;
    }
};

int main()
{
    String  s1( "123" );
    String  s2( "456" );
    String  s3 = s1 + s2;

    cout << s3.s << endl;

    return 0;
}