#include<bits/stdc++.h>
using namespace std;
const long double pi=3.141592653589793238462643383279;
int main(){
  int n;
  double r;
  cin>>n>>r;
  double arr[n][2];
  for(int i=0;i<n;i++){
    for(int j=0;j<2;j++){
      cin>>arr[i][j];
    }
  }
  double ans=0;
  for(int i=0;i<n;i++){
    ans+=sqrt((arr[n][0]-arr[n+1][0])*(arr[n][0]-arr[n+1][0])+(arr[n][1]-arr[n+1][1])*(arr[n][1]-arr[n+1][1]));
  }
  cout<<fixed<<setprecision(2)<<ans+2*r*pi<<endl;
  return 0;
}