using System;
public class Program
{
public static void Main()
Console.WriteLine(PiHexDigit(0));
}
static double PiHexDigit(int k)
return (4d / (8 * k + 1)) - (2d / (8 * k + 4)) - (1d / (8 * k + 5)) - (1d / (8 * k + 6));