1 #include <cstdio>
2 #include <cstring>
3 #include <cmath>
4 #include <algorithm>
5 #define maxn 2000
6 using namespace std;
7 const double pi=acos(-1.0);
8
9 double sqr(double x)
10 {
11 return x*x;
12 }
13 struct node
14 {
15 double x,y;
16 }p[maxn];
17
18 double dis(node a,node b)
19 {
20 return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y));
21 }
22 int main()
23 {
24 int n;
25 double r;
26 scanf("%d%lf",&n,&r);
27 for(int i=0; i<n; i++)
28 {
29 scanf("%lf%lf",&p[i].x,&p[i].y);
30 }
31 p[n]=p[0];
32 double ans=0;
33 for(int i=1; i<=n; i++)
34 {
35 ans+=dis(p[i],p[i-1]);
36 }
37 ans+=pi*r*2;
38 printf("%.2lf\n",ans);
39 return 0;
40 }
