#include<stdio.h>
#include<math.h>
int main()
{
    int n,r,i;
    scanf("%d %d",&n,&r);
    double a[n],b[n],ans,sum=0.0;
    for(i=0; i<n; i++)
    {
        scanf("%lf %lf",&a[i],&b[i]);
    }
    if(n==2)
    {
        sum=sqrt((a[1]-a[0])*(a[1]-a[0])+(b[1]-b[0])*(b[1]-b[0]));
        ans=2.0*3.14159*r;
    }
    else if(n==1)
        ans=2.0*3.14159*r;
    else
    {
        for(i=0,sum=0.0; i<n-1; i++)
        {
            sum=sum+sqrt((a[i]-a[i+1])*(a[i]-a[i+1])+(b[i]-b[i+1])*(b[i]-b[i+1]));
        }
        sum=sum+sqrt((a[n-1]-a[0])*(a[n-1]-a[0])+(b[n-1]-b[0])*(b[n-1]-b[0]));

        ans=2.0*3.14159*r;
    }
    printf("%.2lf\n",ans+sum);

    return 0;
}