#include <string>
using std::string;

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

int main()
{
    string s1 = string("s1");
    const string& s2 = string("s2");
    string& s3 = string("s3");
    
    cout
            << s1 << ", "
            << s2 << ", "
            << s3 << endl;
    return 0;
}