1 #include<iostream>
 2 #include<stdio.h>
 3 #include<math.h>
 4 #include<algorithm>
 5 using namespace std;
 6 #define N 110
 7 struct point
 8 {
 9     double x,y,angel;
10 } p[N],stack[N];
11 int top,n;
12 
13 double dis(point a,point b)
14 {
15     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
16 }
17 
18 bool mult(point p1,point p2,point p0)
19 {
20     return (p1.x-p0.x)*(p2.y-p0.y) >= (p2.x-p0.x)*(p1.y-p0.y);
21 }
22 
23 bool cmp(point a,point b)
24 {
25     if(a.angel == b.angel)
26     {
27         if (a.x == b.x)
28             return a.y > b.y;
29         return a.x > b.x;
30     }
31     return a.angel < b.angel;
32 }
33 
34 void graham()
35 {
36     int i,k=0;
37     for(i=0; i<n; i++)
38         if(p[i].y<p[k].y||((p[i].y==p[k].y)&&(p[i].x<p[k].x)))
39             k=i;
40     swap(p[0],p[k]);
41     for(i=1; i<n; i++)
42         p[i].angel=atan2(p[i].y-p[0].y,p[i].x-p[0].x);
43     sort(p+1,p+n,cmp);
44     stack[0]=p[0];
45     stack[1]=p[1];
46     stack[2]=p[2];
47     top=3;
48     for(i=3; i<n; i++)
49     {
50         while(top > 2 && mult(stack[top-2],stack[top-1],p[i])<=0)
51             top--;
52         stack[top++]=p[i];
53     }
54 }
55 
56 int main()
57 {
58     int i;
59     double ans;
60     while(scanf("%d",&n)!=EOF&&n)
61     {
62         for(i=0; i<n; i++)
63             scanf("%lf%lf",&p[i].x,&p[i].y);
64         if(n==1)
65         {
66             printf("0.00\n");
67             continue;
68         }
69         if(n==2)
70         {
71             printf("%.2lf\n",dis(p[0],p[1]));
72             continue;
73         }
74         graham();
75         ans=0;
76         for(i=0; i<top-1; i++)
77             ans+=dis(stack[i],stack[i+1]);
78         ans+=dis(stack[top-1],stack[0]);
79         printf("%.2lf\n",ans);
80     }
81     return 0;
82 }