#include "iostream"
#include <cmath>
#include <vector>
#include <algorithm>
#include <fstream>

using namespace std;

struct Coord{
    long long int x;
    long long int y;
};

struct DCoord{
    double x;
    double y;
};

Coord Po;
int st = 100000;

bool fun(Coord &a, Coord &b){
    if (((a.y - Po.y) * (b.x - Po.x)) < ((b.y - Po.y) * (a.x - Po.x))){
        return true;
    }
    if (((a.y - Po.y) * (b.x - Po.x)) == ((b.y - Po.y) * (a.x - Po.x))){
        if (sqrt((a.x - Po.x) * (a.x - Po.x) + (a.y - Po.y) * (a.y - Po.y)) < sqrt((b.x - Po.x) * (b.x - Po.x) + (b.y - Po.y) * (b.y - Po.y))){
            return true;
        }

    }
    return false;
}

bool check_left(Coord a, Coord b, Coord c){
    Coord u = {b.x - a.x, b.y - a.y};
    Coord v = {c.x - b.x, c.y - b.y};
    if ((u.x * v.y - u.y * v.x) >= 0){
        return true;
    }
    return false;
}

vector <Coord> graham(vector<Coord> dots){
    Po = dots[0];
    for (int i = 1; i < dots.size(); i++){
        if (dots[i].y < Po.y){
            Po = dots[i];
        }
        else if (Po.y == dots[i].y){
            if (dots[i].x < Po.x){
                Po = dots[i];
            }
        }
    }
    sort(dots.begin(), dots.end(), fun);

    vector<Coord> res;
    res.push_back(dots[0]);
    res.push_back(dots[1]);
    for (int i = 2; i < dots.size(); i++){
        while(!check_left(res[res.size()-2],res[res.size()-1],dots[i])){
            res.pop_back();
        }
        res.push_back(dots[i]);
    }
    return res;
}

double fence_length(vector<Coord> arrr){
    vector <DCoord> arr;
    float dx;
    float dy;
    for (int i = 0; i < arrr.size(); i++){
        dx = arrr[i].x / double(st);
        dy = arrr[i].y / double(st);
        arr.push_back({dx, dy});
    }

    double res = sqrt((arr[0].x - arr[arr.size()-1].x) * (arr[0].x - arr[arr.size()-1].x) + (arr[0].y - arr[arr.size()-1].y) * (arr[0].y - arr[arr.size()-1].y));
    for (int i=0; i<arr.size()-1; i++){
        res += sqrt((arr[i+1].x - arr[i].x) * (arr[i+1].x - arr[i].x) + (arr[i+1].y - arr[i].y) * (arr[i+1].y - arr[i].y));
    }
    return res;
}


int main(){
    vector <Coord> dots;

    ifstream inf;
    inf.open("input.txt");

    int n;
    inf >> n;
    float dx;
    float dy;
    for (int i = 0; i < n; i++) {
        inf >> dx >> dy;
        dots.push_back({int(dx*st), int(dy*st)});
    }
    inf.close();

    ofstream outf;
    outf.open("output.txt");
    outf << fixed;
    outf.precision(5);
    outf << fence_length(graham(dots));
    outf.close();
}