Write a C# Sharp program to create a new string from a given string after swapping last two characters

using System;

namespace exercises
{
   class Program
    {       
        static void Main(string[] args)
        {
            Console.WriteLine(test("Hello"));
            Console.WriteLine(test("Python"));
            Console.WriteLine(test("PHP"));
            Console.WriteLine(test("JS"));
            Console.WriteLine(test("C"));
            Console.ReadLine();
        }

 public static string test(string s1)
        {
          if (s1.Length > 1)
            {
                return s1.Substring(0, s1.Length - 2) + s1[s1.Length - 1] + s1[s1.Length - 2];
            }
            else
            {
                return s1;
            }
        }
   }
}