import java.io.*;
import java.util.*;

public class Main
{

    Pii m = new Pii(0, 0);

    class Pii implements Comparable<Pii>
    {

    int x, y;

    Pii(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    @Override
    public int compareTo(Pii a)
    {
        if (Main.sr(m, this, a))
        {
        return -1;
        }
        return 1;
    }
    }

    static double dist(Pii a, Pii b)
    {
    return Math.sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
    }

    static boolean sr(Pii m, Pii a, Pii b)
    {
    int t = (m.x + a.x) * (m.y - a.y) + (a.x + b.x) * (a.y - b.y) + (b.x + m.x) * (b.y - m.y);
    if (t != 0)
    {
        return t > 0;
    }
    else
    {
        return dist(m, a) > dist(m, b);
    }
    }

    Pii[] a;

    BufferedReader input = new BufferedReader(
        new InputStreamReader(System.in));
    public StringTokenizer stoken = new StringTokenizer("");


    private String nextString() throws IOException {
        while (!stoken.hasMoreTokens()){
            String st = input.readLine();
            stoken = new StringTokenizer(st);
        }
    return stoken.nextToken();
    }

    private int nextInt() throws IOException
    {
    return Integer.parseInt(nextString());
    }

    public void main() throws IOException
    {
    int n = nextInt();
    a = new Pii[n];
    int x, y;
    for (int i = 0; i < n; i++)
    {
        x = nextInt();
        y = nextInt();
        a[i] = new Pii(x, y);
    }
    m = a[0];
    for (int i = 0; i < n; i++)
    {
        if (m.x > a[i].x)
        {
        m = a[i];
        }
        else if (m.x == a[i].x)
        {
        if (m.y > a[i].y)
        {
            m = a[i];
        }
        }
    }
    Arrays.sort(a);
    Pii []v = new Pii[n];
    int vs = 0;
    for (int i = 0; i < n; i++)
    {
        if (vs < 2)
        {
        v[vs]=(a[i]);
        vs++;
        }
        else
        {
        if (!sr(v[vs - 2], v[vs - 1], a[i]))
        {
            vs--;
            i--;
        }
        else
        {
            v[vs] = (a[i]);
            vs++;
        }
        }
    }
    double res = 0;
    for (int i = 0; i < vs - 1; i++)
    {
        res += dist(v[i], v[i + 1]);
    }
    res += dist(v[0], v[vs - 1]);
    System.out.print(res);
    }

    public static void main(String[] args) throws IOException
    {
    Main m = new Main();
    m.main();
    }

}