using System;

public class Program

{

    public static void Main()

    {

        string a = "hello";

        string b = "world";

        swap(ref a, ref b);

        Console.WriteLine(a);

        Console.WriteLine(b);

    }

    public static void swap(ref string a, ref string b)

    {

        string temp = a;

        a=b;

        b=temp;

    }

}