using System;

public class Test
{
	
    static void Swap(ref string a, ref string b) {
        string c = b;
        b = a;
        a = c;
    }
	
	public static void Main()
	{
	    string a = "a";
	    string b = "b";
	    string alsoA = a;
	    Swap(ref a, ref b);
	    Console.WriteLine(a); // B
	    Console.WriteLine(b); // A
	    Console.WriteLine(alsoA); // A
	}
}