/*
 * URAL v1 1020
 * ID : ******
 * 2003 - 05 - 22
 */

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

#define Pi 3.14

typedef struct Nail Nail;
struct Nail
{
  double x;
  double y;
};

double cal(int x,int y)
{
  return sqrt(x*x+y*y);
}

int main()
{
  int N;
  double R,length = 0,curve;
  int i;
  Nail nail[100];

  /* read data */
  scanf("%d %lf",&N,&R);
  for(i = 0;i < N;i++)
    scanf("%lf %lf",&nail[i].x,&nail[i].y);

  curve = 2*Pi*R;
  /* calculate */
  for(i = 0;i < N;i++)
    if(i == N-1)
      length += cal(nail[i].x - nail[0].x,nail[i].y - nail[0].y);
    else
      length += cal(nail[i].x-nail[i+1].x,nail[i].y-nail[i+1].y);

  /*  output */
  printf("%.2f",length+curve);

  return 0;
}