public class Problem {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int r = sc.nextInt();
        double l = 0;
        if (n != 1) {
        double x1 = sc.nextDouble();
        double y1 = sc.nextDouble();
        double memoryX = x1, memoryY = y1;
        for (int i = 1; i <= n; i++) {
            if (i == n) {
                l += Math.sqrt((memoryX - x1) * (memoryX - x1) + (memoryY - y1) * (memoryY - y1));
                continue;
            }
            double x = sc.nextDouble();
            double y = sc.nextDouble();
            l += Math.sqrt((x - memoryX) * (x - memoryX) + (y - memoryY) * (y - memoryY));
            memoryX = x;
            memoryY = y;
        }
        }
        l += 2*Math.PI*r;
        System.out.printf("%.2f", l);
        sc.close();
    }

}

radius can be float number