1 #include <iostream>
 2 #include <algorithm>
 3 #include <cmath>
 4 #include <cstdio>
 5 #include <cstring>
 6 using namespace std;
 7 struct point
 8 {
 9     int x,y;
10 }list[100];
11 int stack[100];
12 int cross(point p0,point p1,point p2)
13 {
14     return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x); 
15 }
16 double dis(point p1,point p2)
17 {
18     return sqrt(double(p2.x-p1.x)*(p2.x-p1.x)+double(p2.y-p1.y)*(p2.y-p1.y));
19 }
20 bool cmp(point p1,point p2)
21 {
22     int tem=cross(list[0],p1,p2);
23     if(tem>0)
24         return 1;
25     else if(tem==0&&dis(list[0],p1)<dis(list[0],p2))
26         return 1;
27     else
28         return 0;
29 }
30 void init(int n)
31 {
32     int i,k;
33     point p0;
34     cin>>list[0].x>>list[0].y;
35     for(i=1;i<n;i++)
36     {
37         cin>>list[i].x>>list[i].y;
38         if(list[i].y<list[0].y||(list[i].y==list[0].y&&list[i].x<list[0].x))
39         {
40             p0=list[0];
41             list[0]=list[i];
42             list[i]=p0;
43         }
44     }
45     sort(list+1,list+n,cmp);
46 }
47 int main()
48 {
49     int i,n;
50     //freopen("in.txt","r",stdin);
51     while(cin>>n&&n)
52     {
53         memset(list,0,sizeof(list));
54         memset(stack,0,sizeof(stack));
55         if(n==1)
56             cout<<0.00<<endl;
57         else if(n==2)
58         {
59             cin>>list[0].x>>list[0].y>>list[1].x>>list[1].y;
60             printf("%0.2f\n",dis(list[0],list[1]));
61         }
62         else
63         {
64             stack[0]=0;
65             stack[1]=1;
66             int top=1;
67             init(n);
68             for(i=2;i<n;i++)
69             {
70                 while(top>0&&cross(list[stack[top]],list[stack[top-1]],list[i])>0)
71                     top--;
72                 top++;
73                 stack[top]=i;
74             }
75             double sum=0;
76             for(i=1;i<=top;i++)
77             {
78                 sum+=dis(list[stack[i]],list[stack[i-1]]);
79             }
80             sum+=dis(list[0],list[stack[top]]);
81             printf("%0.2f\n",sum);
82             }
83         }
84 }