#include<vector>
#include<iostream>
#include<math.h>
using namespace std;
int main()
{
vector<double>x;
vector<double>y;
int n;
double r,t;
cin>>n>>r;
for(int i=0;i<n;i++)
{
cin>>t;
x.push_back(t);
cin>>t;
y.push_back(t);

}

double l=0;
for(int j=0;j<n;j++)
{
if(j==n-1)
l+=sqrt(pow(x[j]-x[0],2)+pow(y[j]-y[0],2));
else
l+=sqrt(pow(x[j+1]-x[j],2)+pow(y[j+1]-y[j],2));



}
double pi=3.14;
l+=r*pi*(n/2);

cout<<l;



return 0;
}