P1007

import java.util.*;
import java.lang.*;
import java.text.*;
import java.io.*;

class pnt{
    double x,y;
    public pnt(double x,double y)
    {
        this.x=x;this.y=y;
    }
};

class problem
{
    public static void main (String[] args) throws java.lang.Exception
    {
        Scanner sc=new Scanner(System.in);
        int n;
        n=sc.nextInt();
        double R;
        R=sc.nextDouble();
        pnt[] p=new pnt[n];
        for (int i=0;i<n;i++)
        {
            double x=sc.nextDouble();
            double y=sc.nextDouble();
            pnt tmp=new pnt(x,y);
            p[i]=tmp;
        }
        double ans=0;
        for (int i=1;i<n;i++)
        {
            double x=p[i].x-p[i-1].x,y=p[i].y-p[i-1].y;
            ans+=Math.sqrt(x*x+y*y);
        }
        if (n>1)
        {
            double x=p[0].x-p[n-1].x,y=p[0].y-p[n-1].y;
            ans+=Math.sqrt(x*x+y*y);
        }
        ans+=2*Math.PI*R;
        DecimalFormat fmt=new DecimalFormat("0.00");
        System.out.println(fmt.format(ans));
    }
}