hdu_1392

#include<iostream>
#include<stdlib.h>
#include<cmath>
#include<stdio.h>
using namespace std;
int n;
typedef struct
{
    double x;
    double y;
}Point;

Point p[110],s[110];

int top;

double Mul(Point a, Point b, Point c)
{
    return (b.x - a.x)*(c.y - a.y) - (b.y - a.y)*(c.x - a.x);
}

double dis(Point a, Point b)
{
    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}


int cmp(const void *a, const void *b)                
{
    Point c = *(Point *)a;
    Point d = *(Point *)b;
    double k = Mul(p[0], c, d);
    if(k < 0 || (!k && dis(c, p[0]) > dis(d, p[0]))) 
        return 1;
    return -1;
} 


void Con()
{
    int i;
    for(i = 1; i < n; i++)
    {
        Point temp;
        if(p[i].y < p[0].y || (p[i].y == p[0].y && p[i].x < p[0].x))
        {
            temp = p[i];
            p[i] = p[0];
            p[0] = temp;
        }
    }
    qsort(p+1, n - 1, sizeof(p[0]), cmp);
    s[0] = p[0];        
    s[1] = p[1];
    s[2] = p[2];
    top =2;
    
    for(i = 3; i < n; i++)//congsan
    {
        while(top >= 2 && Mul(s[top - 1], s[top], p[i]) <= 0) 
            top--;
        top++;
        s[top] = p[i];
    }
}


int main()
{
    
    while(cin>>n,n)
    {
        int i;
        for(i = 0; i < n; i++)
        {
            cin>>p[i].x>>p[i].y;
        }
        if(n == 1)
        {
            cout<<"0.00"<<endl;
            continue;
        }
    
        else if(n == 2)
        {
            printf("%.2lf\n",dis(p[0],p[1]));
            continue;
        }
        Con();
        double count = 0;
        for(i = 0; i < top; i++)
        {
            count += dis(s[i],s[i+1]);
        }
        count += dis(s[top],s[0]);
        printf("%.2lf\n",count);

    }
    return 0;
}