#include <iostream>
#include <math.h>
#include <iomanip>
using namespace std;

void main()
{
    double x[99],y[99],r,n,dlina[99];
    cin >> n >> r;
    double P=2*3.14*r;
    for (int i=0; i<=n-1; i++)
    {
        cin >> x[i] >> y[i];
    }
    for (int j=0; j<=n-1; j++)
    {
        if (j!=(n-1))
        {
            dlina[j]=sqrt((x[j]-x[j+1])*(x[j]-x[j+1])+(y[j]-y[j+1])*(y[j]-y[j+1]));
            P+=dlina[j];
        }
        else
        {
            dlina[j]=sqrt((x[j]-x[0])*(x[j]-x[0])+(y[j]-y[0])*(y[j]-y[0]));
            P+=dlina[j];
        }
    }
    cout << setprecision(2) << setiosflags (ios::showpoint | ios::fixed) << P;

}