1020. Rope

#include<bits/stdc++.h>
using namespace    std;

#define flush        cin.ignore(numeric_limits<streamsize>::max(),'\n')
#define fasterio     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define NL           printf("\n")



//who cares? I want to give some scary looks to my code... XD//


typedef long long int       ll;
typedef double              dl;
typedef unsigned long long  ul;

// ------------------------------------Constants-------------------------------------//

#define pi           (acos(-1.0)) //3.1415926535897932384626
#define mx           7500000
#define dpoint(x)    fixed<<setprecision(x)
#define mod          1000000007
#define pb(x)        push_back(x)
#define scn(x)       scanf("%d",&x)
#define scnd(x)      scanf("%lf",&x)


// --------------------------Pre made Functions & Proto Type--------------------------//

template <class T> T gcd(T a, T b){if(a == 0) return b;return gcd ( b%a, a );}
template <class T> T lcm(T a, T b){return ( ( a/gcd ( a, b ) )*b );}
template <class T> T digitsum(T n){T sum=0;while(n!=0){sum+=n%10;n/=10;}return sum;}

void print(int n, int c){
  if(c==n+1) return;
  print(n,c+1);
  cout<<c<<" ";

}


 // --------------------------------------Global--------------------------------------//


 // -------------------------------------slove----------------------------------------//
 //Code Status :ac ;name: Unlucky Bird;
int main()
{
    #ifndef ONLINE_JUDGE
        freopen("int.txt","r",stdin);
        freopen("ans2.txt","w",stdout);
    #endif
         int n,r;
         cin>>n>>r;
         std::vector<dl> first;
         std::vector<dl> secound;
         for(int i=0; i<n; i++){
            dl x,y;
            cin>>x>>y;
            first.pb(x);
            secound.pb(y);
         }
         dl d = sqrt(((first[0]-first[n-1])*(first[0]-first[n-1]))+((secound[0]-secound[n-1])*(secound[0]-secound[n-1])));

         for(int i=0; i<n-1; i++){
            d += sqrt(((first[i]-first[i+1])*(first[i]-first[i+1]))+((secound[i]-secound[i+1])*(secound[i]-secound[i+1])));
         }
         dl ans = d+(2*pi*r);
         cout<< dpoint(2)<<ans<<endl;

    return 0;
}
/// ----------------------------Funaction Descriptions----------------------------------//


//author anikaksh;
//trust me ur the competitor of your own, not ur friend!
//Thanks To My Seniors and frndzz who help me all the time's
//Contest link:https://lightoj.com/problem/1311?problem=1311