#include <stdio.h>
#include <math.h>

int main()
{
    float ans,r,x[100], y[100];
    int n,i;
    scanf("%d %f", &n, &r);
    for (i = 0; i < n; i++)
    scanf("%f %f", &x[i], &y [i]);
    ans = 2*r*3.14159;
    if (n > 1)
    {
    for (i = 0; i < n-1; i++)
    ans += sqrt( (x[i]-x[i+1])*(x[i]-x[i+1]) + (y[i]-y[i+1]) * (y
[i]-y[i+1]));
    ans += sqrt( (x[n]-x[1])*(x[n]-x[1]) + (y[n]-y[1]) * (y[n]-y
[1]));
    }
    printf("%.2f\n", ans);
    return 0;
}