1 //极角排序
2 #include <bits/stdc++.h>
3 #define sqr(x) ((x)*(x))
4 using namespace std;
5 int n,st[200001],top;
6 struct POI
7 {
8 int x,y;
9 POI()
10 {
11 x=y=0;
12 }
13 POI(int _x,int _y)
14 {
15 x=_x;y=_y;
16 }
17 } p[200001];
18 int cross(POI x,POI y)
19 {
20 return x.x*y.y-x.y*y.x;
21 }
22 double dis(POI x,POI y)
23 {
24 return sqrt(sqr(x.x-y.x)+sqr(x.y-y.y));
25 }
26 POI operator-(POI x,POI y)
27 {
28 return POI(x.x-y.x,x.y-y.y);
29 }
30 bool com(POI x,POI y)
31 {
32 return(cross(x-p[1],y-p[1])>0 || cross(x-p[1],y-p[1])==0 && dis(x,p[1])<dis(y,p[1]));
33 }
34 int main()
35 {
36 for(scanf("%d",&n);n;scanf("%d",&n))
37 {
38 for(int i=1;i<=n;i++)
39 scanf("%d%d",&p[i].x,&p[i].y);
40 if(n==2)//wtf
41 {
42 printf("%.2f\n",dis(p[1],p[2]));
43 continue;
44 }
45 int id=1;
46 for(int i=2;i<=n;i++)
47 if(p[i].x<p[id].x || p[i].x==p[id].x && p[i].y<p[id].y) id=i;
48 swap(p[1],p[id]);
49 sort(p+2,p+n+1,com);
50 st[top=1]=st[0]=1;
51 for(int i=2;i<=n;i++)
52 {
53 while(top && cross(p[st[top]]-p[st[top-1]],p[i]-p[st[top]])<0) --top;
54 st[++top]=i;
55 }
56 double len=0;
57 // puts("");
58 // for(int i=1;i<=top;i++)
59 // printf("%d %d\n",p[st[i]].x,p[st[i]].y);
60 st[++top]=1;
61 for(int i=1;i<top;i++)
62 len+=dis(p[st[i]],p[st[i+1]]);
63 printf("%.2f\n",len);
64 }
65 return 0;
66 }
