using System;

public class Program

{

    public static void Main()

    {

        int n = 100000000;

        double count = 0;

        for (int i = 1; i < n; i++) 

        {

            count += Math.PI * Math.Sin(Math.PI + i * Math.PI / (2 * n)) / (2 * n);

        }

        Console.WriteLine(count);

    }

}