#include<cmath>

 #include<cstdio>

 #include<algorithm>

 using namespace std;

 #define MAXN 100+10

 struct Point{

     double x, y;

     Point(double x = , double y = ): x(x), y(y){}

     void scan(){

         scanf("%lf %lf", &x, &y);

     }

 };

 typedef Point Vector;

 Vector operator - (Vector A, Vector B){

     return Vector(A.x - B.x, A.y - B.y);

 }

 double dot(Vector A, Vector B){//点乘

     return A.x * B.x + A.y * B.y;

 }

 double length(Vector A){//向量模

     return sqrt(dot(A, A));

 }

 double cross(Vector A, Vector B){//叉乘

     return A.x * B.y - A.y * B.x;

 }

 int n;

 Point p[MAXN], stack[MAXN];

 bool input(){

     scanf("%d", &n);

     if(n == ) return false;

     for(int i = ; i < n; ++i){

         p[i].scan();

     }

     return true;

 }

 bool cmp(Point A, Point B){

     return A.x < B.x || (A.x == B.x && A.y < B.y);

 }

 int convex_hull(){//Adrew算法 求凸包

     sort(p, p + n, cmp);

     int m = ;

     for(int i = ; i < n; ++i){

         while(m >  && cross(stack[m - ] - stack[m - ], p[i] - stack[m - ]) <= ) --m;

         stack[m ++] = p[i];

     }

     int k = m;

     for(int i = n - ; i >= ; --i){

         while(m > k && cross(stack[m - ] - stack[m - ], p[i] - stack[m - ]) <= ) --m;

         stack[m ++] = p[i];

     }

     if(n > ) --m;

     return m;

 }

 void solve(){

     n = convex_hull();

     if(n == ){//当只有一个点时，绳子长度为0

         puts("0.00");

         return ;

     }

     if(n == ){//当只有两个点时，绳子长度为两点之间的长度

         printf("%.2lf\n", length(stack[] - stack[]));

         return ;

     }

     double ans = ;//绳子的累加长度

     stack[n] = stack[];//为了算第n点到第1点的距离

     for(int i = ; i < n; ++i){

         ans += length(stack[i] - stack[i + ]);

     }

     printf("%.2lf\n", ans);

 }

 int main(){

     while(input()){

         solve();

     }

     return ;

 }