1392

#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<stack>
#include<iomanip>
#include<cctype>
#include<climits>
#include<queue>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

struct P
{
    int x,y;
};


const int maxn=50050;
int n,k;
P ps[maxn];

bool cmp(const P& p,const P& q)
{
    if(p.x!=q.x)
        return p.x<q.x;
    return p.y<q.y;
}

int cross(P p0,P p1,P p2)
{
    return (p2.x-p0.x)*(p1.y-p0.y)-(p1.x-p0.x)*(p2.y-p0.y);
}

vector<P> convex_hull(P* ps,int n)
{
    sort(ps,ps+n,cmp);
    k=0;
    vector<P> qs(n*2);
    for(int i=0;i<n;i++){
        while(k>1 && cross(qs[k-2],qs[k-1],ps[i])<=0)
            k--;
        qs[k++]=ps[i];
    }
    for(int i=n-2,t=k;i>=0;i--){
        while(k>t && cross(qs[k-2],qs[k-1],ps[i])<=0)
            k--;
        qs[k++]=ps[i];
    }
    k--;
    qs.resize(k);
    return qs;
}

double dis(P p,P q)
{
    double dist=(p.x-q.x)*(p.x-q.x)+(p.y-q.y)*(p.y-q.y);
    return sqrt(dist);
}


int main()
{
    while(~scanf("%d",&n)){
        if(n==0)
            return 0;
        for(int i=0;i<n;i++)
            scanf("%d %d",&ps[i].x,&ps[i].y);
        vector<P> qs=convex_hull(ps,n);
        double ans=0;
        if(k==0||k==1)
            printf("0
");
        else if(k==2)
            printf("%.2lf
",dis(qs[0],qs[1]));
        else{
            for(int i=0;i<k-1;i++)
                ans+=dis(qs[i],qs[i+1]);
            ans+=dis(qs[0],qs[k-1]);
            printf("%.2lf
",ans);
         }
    }
    return 0;
}