using System;

public class Program

{

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

    {

        int temp = a;

        a = b;

        b = temp;

    }

    public static void Main()

    {

        int one = 1;

        int thirteen = 13;

        swap(ref one, ref thirteen);

        Console.WriteLine($"one: {one}\nthirteen: {thirteen}");

    }

}