NumberFormatInfo nfi = NumberFormatInfo.InvariantInfo;
            string nailsNradius = Console.ReadLine();
            string[] NailsNradius = nailsNradius.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
            int nails = Int32.Parse(NailsNradius[0]);
            int radius = Int32.Parse(NailsNradius[1]);
            double length=0;
            string temp;

            for (int i = 0; i < nails; i++)
            {
                string tempInput = Console.ReadLine();
                string[] coordinates = tempInput.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

//calculating the sum (here length is sum)
                length += Double.Parse(coordinates[0]) + Double.Parse(coordinates[1]);
//converting it to two digits precision
                temp = string.Format(nfi, "{0:F2}",length.ToString());
                length = Double.Parse(temp);
            }
//finally printing the length + 2*PI*r with 2 digit precision
            Console.WriteLine(string.Format(nfi, "{0:F2}", length+(2*Math.PI*radius)));