#include<bits/stdc++.h>
using namespace std;
const double pai=3.1415926535;
double x[105],y[105];
int n;
double r;
double jvli(int x,int x1,int y,int y1)
{
	double a=1.0*sqrt(pow(abs(x1-x),2) + pow(abs(y1-y),2));
	return a;
}
double c1=2*r*pai,c2=0;
int main()
{
	cin>>n>>r;
    for(
	int i=1; i<=n; i++)
        cin>>x[i]>>y[i];
    for(int i=2; i<=n; i++)
        c1+=jvli(x[i-1],x[i],y[i],y[i-1]);
    c2=jvli(x[n],x[1],y[n],y[1]);
    printf("%.2f",c1+c2);
	return 0;
}