1 /******************************
  2 code by drizzle
  3 blog: www.cnblogs.com/hsd-/
  4 ^ ^    ^ ^
  5  O      O
  6 ******************************/
  7 #include<bits/stdc++.h>
  8 #include<map>
  9 #include<set>
 10 #include<cmath>
 11 #include<queue>
 12 #include<bitset>
 13 #include<math.h>
 14 #include<vector>
 15 #include<string>
 16 #include<stdio.h>
 17 #include<cstring>
 18 #include<iostream>
 19 #include<algorithm>
 20 #pragma comment(linker, "/STACK:102400000,102400000")
 21 using namespace std;
 22 #define  A first
 23 #define B second
 24 const int mod=1000000007;
 25 const int MOD1=1000000007;
 26 const int MOD2=1000000009;
 27 const double EPS=0.00000001;
 28 typedef __int64 ll;
 29 const ll MOD=1000000007;
 30 const int INF=1000000010;
 31 const ll MAX=1ll<<55;
 32 const double eps=1e-8;
 33 const double inf=~0u>>1;
 34 const double pi=acos(-1.0);
 35 typedef double db;
 36 typedef unsigned int uint;
 37 typedef unsigned long long ull;
 38 struct point
 39 {
 40     double x,y;
 41     point(double x=0,double y=0):x(x),y(y) {}
 42 };
 43 typedef point vec;
 44 vec operator -(point a,point b)
 45 {
 46     return vec(a.x-b.x,a.y-b.y);
 47 }
 48 vec operator +(point a,point b)
 49 {
 50     return vec(a.x+b.x,a.y+b.y);
 51 }
 52 vec operator *(point a,double t)
 53 {
 54     return vec(a.x*t,a.y*t);
 55 }
 56 vec operator /(point a,double t)
 57 {
 58     return vec(a.x/t,a.y/t);
 59 }
 60 int dcmp(double x)
 61 {
 62     if(fabs(x)<=eps) return 0;
 63     return x<0?-1:1;
 64 }
 65 double cross(vec a,vec b)  ///叉积
 66 {
 67     return a.x*b.y-a.y*b.x;
 68 }
 69 bool cmp(point a,point b)
 70 {
 71     if(fabs(a.x-b.x)<=eps) return a.y<b.y;
 72     return a.x<b.x;
 73 }
 74 double disn(point a,point b)
 75 {
 76     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
 77     /*两点之间的距离*/
 78 }
 79 void convexhull(point *s,int &n)
 80 {
 81     sort(s,s+n,cmp);
 82     int m=0;
 83     point p[110];
 84     for(int i=0; i<n; i++)
 85     {
 86         while(m>1 && dcmp(cross(p[m-1]-p[m-2],s[i]-p[m-2]))<=0)
 87             m--;
 88         p[m++]=s[i];
 89     }
 90     int k=m;
 91     for(int i=n-2; i>=0; i--)
 92     {
 93         while(m>k && dcmp(cross(p[m-1]-p[m-2],s[i]-p[m-2]))<=0)
 94             m--;
 95         p[m++]=s[i];
 96     }
 97     m--;
 98     n=m;
 99     for(int i=0; i<n; i++) s[i]=p[i];
100     /*建立凸包*/
101 }
102 int jishu;
103 int main()
104 {
105     while(scanf("%d",&jishu)!=EOF)
106     {
107         if(jishu==0)
108             break;
109         point s[110];
110         for(int i=0; i<jishu; i++)
111         {
112             scanf("%lf %lf",&s[i].x,&s[i].y);
113 
114         }
115         if(jishu==1)
116         {
117             printf("0.00\n");
118                 continue;
119         }
120         if(jishu==2)
121         {
122             printf("%.2f\n",disn(s[0],s[1]));
123                continue;
124         }
125         convexhull(s,jishu);
126         double sum=0;
127         for(int i=0; i<jishu-1; i++)
128         {
129             sum+=disn(s[i],s[i+1]);
130         }
131         sum+=disn(s[jishu-1],s[0]);
132         printf("%.2f\n",sum);
133     }
134     return 0;
135 }