#include<bits/stdc++.h>
using namespace std;
struct zuobiao{
	double x,y;
}shu[1000];
double daan;
double pi=3.14159265;
double zhi(zuobiao a,zuobiao b){
	return sqrt(pow(a.x-b.x,2)+pow(b.y-a.y,2));
}
int main(){
	int n;
	double q;
	cin>>n>>q;
	daan+=q*2*pi;
	for(int i=0;i<n;i++){
		cin>>shu[i].x>>shu[i].y;
	}
	for(int i=0;i<n-1;i++){
		daan+=zhi(shu[i],shu[i+1]);
	}
	daan+=zhi(shu[0],shu[n-1]);
	cout<<fixed<<setprecision(2)<<daan;
}