#include <iostream>

#include <cstdio>

#include <cstring>

#include <cmath>

#include <algorithm>

#define N 100005

#define eps 1e-8

using namespace std;

struct point

{

    double x, y;

    point(){}

    point(double a, double b):x(a), y(b){}

    point operator-(point a){//向量减法

        return point(x-a.x, y-a.y);

    }

    point operator+(point a){//向量加法

        return point(x+a.x, y+a.y);

    }

    double operator*(point a){//向量叉积

        return x*a.y-y*a.x;

    }

    bool operator<(const point a)const{

        if(fabs(x-a.x)<eps)return y<a.y;//浮点数的判等不能直接用‘==’直接比较

        return x<a.x;

    }

    bool operator==(const point a)const{

        return (fabs(x-a.x)==eps && fabs(y-a.y));

    }

    double len(){//向量的模

        return sqrt(x*x+y*y);

    }

}p[N], s[N];//p为点，s为栈

double cp(point a, point b, point o)//向量oa，ob叉积

{

    return (a-o)*(b-o);

}

void Convex(point *p, int &n)//Graham扫描法，栈内为所有凸包点

{

    sort(p, p+n);

    int top, m;

    s[0] = p[0]; s[1] = p[1]; top = 1;

    for(int i = 2; i < n; i++)//从前往后扫

    {

        while(top>0 && cp(p[i], s[top], s[top-1])>=0)top--;

        s[++top] = p[i];

    }

    m = top;

    s[++top] = p[n-2];

    for(int i = n-3; i >= 0; i--)//从后往前扫

    {

        while(top>m && cp(p[i], s[top], s[top-1])>=0)top--;

        s[++top] = p[i];

    }

    n = top;

}

int main()

{

    int n;

    while(scanf("%d", &n)!=EOF && n)

    {

        for(int i = 0; i < n; i++)

              scanf("%lf%lf", &p[i].x, &p[i].y);

        sort(p, p+n);

        int cnt=unique(p, p+n) - p;

        if(cnt == 1){

            printf("0.00\n");continue;

        }else if(cnt==2){

            printf("%.2lf\n", (p[1]-p[0]).len());continue;

        }

        Convex(p, cnt);

        double ans = 0;

        s[cnt] = s[0];

        for(int i = 0; i < cnt; i++)ans+=(s[i+1]-s[i]).len();

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

    }

    return 0;

}