Write a C# Sharp program to create a new string using two given strings s1, s2, the format of the new string will be s1s2s2s1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace exercises
{
   class Program
    {       
        static void Main(string[] args)
        {
            Console.WriteLine(test("Hi", "Hello"));
            Console.WriteLine(test("whats", "app"));
            Console.ReadLine();
        }
        
         public static string test(string s1, string s2)
         {
            return s1 + s2 + s2 + s1;
         }
  }
}