#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
#include <cstdio>

using namespace std;

#define pii pair<int,int>
#define mp make_pair
#define fi first
#define se second

pii a[1000];
pii m;

double dist(pii a, pii b)
{
    return sqrt((a.fi-b.fi)*(a.fi-b.fi) + (a.se-b.se)*(a.se-b.se));
}

bool sr(pii m, pii a, pii b)
{
    int t = (m.fi-a.fi)*(m.se+a.se)+(a.fi-b.fi)*(a.se+b.se)+(b.fi-m.fi)*(b.se+m.se);
    if (t != 0)
    {
        return t > 0;
    }
    else
    {
        return dist(m,a) > dist(m,b);
    }
}

bool srr(pii a, pii b)
{
    return sr(m,a,b);
}

int main()
{
    int n,x,y;
    scanf("%d",&n);
    for (int i = 0; i < n; i++)
    {
        scanf("%d%d",&x,&y);
        a[i] = mp(x,y);
    }
    m = a[0];
    for (int i = 0; i < n; i++)
    {
        if (m.fi > a[i].fi)
        {
            m = a[i];
        }
        else if (m.fi == a[i].fi && m.se > a[i].se)
        {
            m = a[i];
        }
    }
    sort(a,a+n,srr);
    vector<pii> v;
    for (int i = 0; i < n; i++)
    {
        if (v.size() < 2)
        {
            v.push_back(a[i]);
        }
        else
        {
            if (!sr(v[v.size()-2],v[v.size()-1],a[i]))
            {
                v.pop_back();
                i--;
            }
            else
            {
                v.push_back(a[i]);
            }
        }
    }
    double res = 0;
    for (int i = 0; i < v.size()-1; i++) res += dist(v[i],v[i+1]);
    res += dist(v[0],v[v.size()-1]);
    cout.precision(20);
    cout << res;
    return 0;
}