using System;

public class Program

{

    public static void Main(string[] args)

    {

        Console.WriteLine("Hello World");

        Console.Write("Введите L: ");

        int L = Convert.ToInt32(Console.ReadLine());        

        double R = L / 2 * Math.PI;

​

        double Sokr = Math.PI * Math. Pow(R, 2);

        double akvad = Math. Sqrt(Sokr);

        Console.WriteLine("L = {0}, R = {1}, Sokr = {2}, akvad = {3}", L, R, Sokr, akvad);

        Console.ReadLine();

    }

}