import Data.List

import Debug.Trace

import Text.Printf

findBottomLeftMostPoint = foldl1

(\(x, y) (x', y') ->

if y' < y || (y' == y && x' < x) then (x', y') else (x, y)

)

dist (x1, y1) (x2, y2) = sqrt $ (x2 - x1) ^ 2 + (y2 - y1) ^ 2

orientationComparer ref@(x0, y0) p1@(x1, y1) p2@(x2, y2) =

let angle1 = atan2 (y1 - y0) (x1 - x0)

angle2 = atan2 (y2 - y0) (x2 - x0)

in if abs (angle2 - angle1) < 1e-6

then compare (dist ref p1) (dist ref p2)

else compare angle1 angle2

calcOrientation (x1, y1) (x2, y2) (x3, y3) =

x1 * y2 - x2 * y1 + x3 * y1 - x1 * y3 + x2 * y3 - x3 * y2

addPoint :: [(Double, Double)] -> (Double, Double) -> [(Double, Double)]

addPoint [] v = [v]

addPoint vs@[p] v = v : vs

addPoint vs@(p1 : p2 : ps) v =

if calcOrientation p2 p1 v < 0 then addPoint (p2 : ps) v else v : vs

convexHull = foldl addPoint []

calcHullLength :: [(Double, Double)] -> Double

calcHullLength points =

let base = findBottomLeftMostPoint points

polygon =

[base]

++ sortBy (orientationComparer base) (delete base points)

++ [base]

hull = convexHull polygon

in traceShow polygon $ traceShow hull $ sum $ zipWith dist

(init hull)

(tail hull)

main :: IO ()

main = do

n <- readLn :: IO Int

content <- getContents

let points =

map (\[x, y] -> (x, y))

. map (map (read :: String -> Double))

. map words

. lines

$ content

ans = calcHullLength points

printf "%.1f\n" ans