#include <algorithm>

#include  <iterator>

#include  <iostream>

#include   <cstring>

#include   <cstdlib>

#include   <iomanip>

#include    <bitset>

#include    <cctype>

#include    <cstdio>

#include    <string>

#include    <vector>

#include     <stack>

#include     <cmath>

#include     <queue>

#include      <list>

#include       <map>

#include       <set>

#include   <cassert>

using namespace std;

//#pragma GCC optimize(3)

//#pragma comment(linker, "/STACK:102400000,102400000")  //c++

#define lson (l , mid , rt << 1)

#define rson (mid + 1 , r , rt << 1 | 1)

#define debug(x) cerr << #x << " = " << x << "\n";

#define pb push_back

#define pq priority_queue

typedef long long ll;

typedef unsigned long long ull;

typedef pair<ll ,ll > pll;

typedef pair<int ,int > pii;

typedef pair<int,pii> p3;

//priority_queue<int> q;//这是一个大根堆q

//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q

#define fi first

#define se second

//#define endl '\n'

#define OKC ios::sync_with_stdio(false);cin.tie(0)

#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行

#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)

//priority_queue<int ,vector<int>, greater<int> >que;

const ll mos = 0x7FFFFFFF;  //

const ll nmos = 0x80000000;  //-2147483648

const int inf = 0x3f3f3f3f;

const ll inff = 0x3f3f3f3f3f3f3f3f; //

const int mod = ;

const double esp = 1e-;

const double PI=acos(-1.0);

template<typename T>

inline T read(T&x){

    x=;int f=;char ch=getchar();

    while (ch<''||ch>'') f|=(ch=='-'),ch=getchar();

    while (ch>=''&&ch<='') x=x*+ch-'',ch=getchar();

    return x=f?-x:x;

}

/*-----------------------showtime----------------------*/

            const int maxn = ;

            struct node

            {

                int x,y;

            }p[maxn],s[maxn];

            inline bool cmp(node a,node b){

                double A = atan2((a.y - p[].y) , (a.x - p[].x));

                double B = atan2((b.y - p[].y) , (b.x - p[].x));

                if(A != B) return A < B;

                else return a.x < b.x;

            }

            ll Cross (node a,node b,node c){

                return 1ll*(b.x - a.x)*(c.y - a.y) - 1ll*(b.y - a.y)*(c.x - a.x);

            }

            int top,n;

            void Get(){

                p[] = (node){inf,inf}; int k;

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

                    if(p[].y > p[i].y || (p[].y == p[i].y && p[i].x < p[].x))

                    {

                        p[] = p[i];    k = i;

                    }

                swap(p[k], p[]);

                sort(&p[] , &p[n+], cmp);

                s[] = p[] , s[] = p[], top = ;

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

                    if(top && Cross(s[top-] ,p[i], s[top]) >= )

                        top--;

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

                }

            }

            double dis(node a,node b){

                return sqrt((a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y));

            }

int main(){     

            while(~scanf("%d", &n) && n){

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

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

                }

                Get();

                double ans = ;

                if(top == ){

                    ans = ;

                }

                else if(top == ){

                    ans = dis(s[],s[]);

                }

                else {

                    s[++top] = s[];

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

                        ans += dis(s[i], s[i+]);

                    }

                }

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

            }

            return ;

}