//Rextester.Program.Main is the entry point for your code. Don't change it.

//Microsoft (R) Visual C# Compiler version 2.9.0.63208 (958f2354)

​

using System;

​

namespace Rextester

{

    public class Program

    {

        public static void Main(string[] args)

        {

            Console.WriteLine(Switch("Петров Иван"));

            Console.WriteLine(Switch("Петров"));

            Console.WriteLine(Switch("Петров Иван Сергеевич"));

            Console.WriteLine(Switch("Петров Иван Люк оглы"));

        }

        private static string Switch(string fullname) {

            var firstSpace = fullname.IndexOf(' ');

            string name;

            if (firstSpace != -1)

            {

                name = string.Format("{0} {1}", fullname.Substring(firstSpace + 1), fullname.Substring(0, firstSpace));

            }

            else

            {

                name = fullname;

            }

            return name;

        }

    }

}