#include<bits/stdc++.h>
using namespace std;
double pi=acos(-1.);
int main()
{
    int n,a,i;
    double x[200],y[200],s=0.0,m,s1;
    scanf("%d %lf",&n,&m);
    for(i=0;i<n;i++)
    {
        scanf("%lf %lf",&x[i],&y[i]);
    }
    for(i=0;i<n;i++)
    {
        if(i==n-1)
            break;
        s=s+sqrt(((x[i]-x[i+1])*(x[i]-x[i+1]))+((y[i]-y[i+1])*(y[i]-y[i+1])));
    }
    s=s+sqrt(((x[0]-x[n-1])*(x[0]-x[n-1]))+((y[0]-y[n-1])*(y[0]-y[n-1])));
    s1=(2*pi*m)/(double)n;
    printf("%.2lf\n",s+(n*s1));
}