#include <iostream>
# include <cmath>

using namespace std;

int main()
{
    int a=0;
    cin>>a;
    int o=0;
    cin>>o;
    double r=0;
    double p[a][2];
    double n = (2 * M_PI)* o;
    for(int i=0;i<a;i++)
    cin>>p[i][0]>>p[i][1];

    for(int i=0;i<a;i++)
        r+=sqrt((p[i][0]-p[i-1][0])*(p[i][0]-p[i-1][0]) + (p[i][1]-p[i-1][1])*(p[i][1]-p[i-1][1]));

    r=r+n;
    r+=sqrt((p[0][0]-p[a-1][0])*(p[0][0]-p[a-1][0]) + (p[0][1]-p[a-1][1])*(p[0][1]-p[a-1][1]));
    cout<<round(r*100)/100;
}