C#: Create a new string with the last char added at the front and back of a given string of length 1 or more

using System;

// Namespace declaration
namespace exercises
{
    // Class declaration
    class Program
    {
        // Main method - entry point of the program
        static void Main(string[] args)
        {
            // Calling the 'test' method with different strings and displaying the returned values
            Console.WriteLine(test("Red"));   // Output: "dRedd"
            Console.WriteLine(test("Green")); // Output: "nGreenn"
            Console.WriteLine(test("1"));     // Output: "11"
            Console.ReadLine();                // Keeping the console window open
        }

        // Method to perform a specific string transformation
        public static string test(string str)
        {
            // Extracts the last character of the input string
            var s = str.Substring(str.Length - 1);

            // Concatenates the last character, the input string, and the last character again
            return s + str + s;
        }
    }
}