#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <math.h>
#include <iomanip>

using namespace std;

int main()
{
    setlocale (LC_ALL, "Russian");
    int N;
    double R;
    const double PI = acos(-1.0);
    cin >> N >> R;
    if((N < 1) || (N > 100)) exit(0);
    if(R<=0) exit(0);

    double a[101][2];

    for(int i = 0; i < N; i++)
    {
        for(int j = 0; j < 2; j++)
        {
            cin >> a[i][j];
        }
    }
    a[N][0] = a[0][0];
    a[N][1] = a[0][1];
    a[N+1][0] = a[1][0];
    a[N+1][1] = a[0][1];
    a[N+2][0] = a[2][0];
    a[N+2][1] = a[2][1];

    double dLength = 0.0,
           dSide1,
           dSide2,
           dSide3,
           dCurve,
           alpha;
    for(int i = 0; i < N; i++)
    {
        dSide1 = 0.0;
        dSide2 = 0.0;
        dSide3 = 0.0;
        dCurve = 0.0;
        for(int j = 0; j < 2; j++)
        {
            dSide1 += (a[i][j] - a[i+1][j])*(a[i][j] - a[i+1][j]);
            dSide2 += (a[i+1][j] - a[i+2][j])*(a[i+1][j] - a[i+2][j]);
            dSide3 += (a[i][j] - a[i+2][j])*(a[i][j] - a[i+2][j]);
        }
        dSide1 = sqrt(dSide1);
        dSide2 = sqrt(dSide2);
        dSide3 = sqrt(dSide3);
        alpha = (dSide3*dSide3 - (dSide1*dSide1 + dSide2*dSide2)) / (-2*dSide1*dSide2);
        alpha = PI / 2 - alpha;
        alpha = alpha * 180/PI;
        dCurve = 2 * PI * R * (180 - alpha) / 360;
        dLength += dSide1 + dCurve;
    }

    if (N == 1) dLength = 2 * PI * R;
    if (N == 2) dLength = 2 * PI * R + 2 * dSide1;

    cout << setprecision(2) << setiosflags (ios::showpoint | ios::fixed) << dLength;
    return 0;
}