using System;
class Program
{
    private static void Main()
    {
        string[] s = Console.ReadLine().Split(' ');
        int n = int.Parse(s[0]), r = int.Parse(s[1]);
        double S_Ay = System.Math.PI * r * 2;
        string[] s2 = Console.ReadLine().Split(' ');
        double a1 = double.Parse(s2[0]);
        double b1 = double.Parse(s2[1]);
        if (n > 1)
        {
            double aa = a1;
            double bb = b1;
            for (int i = 2; i <= n; i++)
            {
                string[] s3 = Console.ReadLine().Split(' ');
                double a2 = double.Parse(s3[0]);
                double b2 = double.Parse(s3[1]);
                S_Ay += System.Math.Sqrt(System.Math.Pow(a2 - a1, 2) + System.Math.Pow(b2 - b1, 2));
                a1 = a2;
                b1 = b2;
            }
            S_Ay += System.Math.Sqrt(System.Math.Pow(a1 - aa, 2) + System.Math.Pow(b1 - bb, 2));
        }
        Console.WriteLine("{0:F2}",S_Ay);
    }
}

Edited by author 21.08.2011 11:30

R should be a double type, not integer.