#include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
double distance(double x1, double y1, double x2, double y2);
int main(){
int n ; double r;
cin>>n>>r;
double x1,y1,x2,y2;
cin>>x1>>y1;
cin>>x2>>y2;
double ans = 0;
//float pi = (float)22/(float)7;
double pi=2*acos(0.0);
//cout<<pi<<endl;
ans = distance(x1,y1,x2,y2);
//cout<<ans<<endl;
int temp = n;
temp = temp-2;
double x3,y3;
x3=x2;
y3=y2;
while(temp>0){
x2=x3;
y2=y3;
cin>>x3>>y3;
ans = ans + distance(x2,y2,x3,y3);
// cout<<ans<<endl;
temp--;
}
ans = ans + distance(x1,y1,x3,y3); //distance of last and first point
double con = 2*pi*r;
ans = ans + con;
cout.precision(2);
cout<<fixed<<ans<<endl;
return 0;
}
double distance(double x1, double y1, double x2, double y2){
x1 = x1-x2;
y1 = y1-y2;
x1 = x1*x1;
y1 = y1*y1;
double sum = x1+y1;
sum = sqrt(sum);
return sum;
}
