import Data.List

-- Data structure to represent points
type Point = (Double, Double)

-- Cross product of three points
crossProduct :: Point -> Point -> Point -> Double
crossProduct (x1, y1) (x2, y2) (x3, y3) = (x2 - x1) * (y3 - y1) - (y2 - y1) * (x3 - x1)

-- Calculate the distance between two points
distance :: Point -> Point -> Double
distance (x1, y1) (x2, y2) = sqrt ((x2 - x1) ^ 2 + (y2 - y1) ^ 2)

-- Find the convex hull of a list of points
convexHull :: [Point] -> [Point]
convexHull points = let sortedPoints = sort points
                        lowerHull = buildHull sortedPoints
                        upperHull = buildHull (reverse sortedPoints)
                    in lowerHull ++ tail upperHull

-- Build the convex hull from a sorted list of points
buildHull :: [Point] -> [Point]
buildHull = foldl addPoint []
    where addPoint [] p = [p]
          addPoint [h] p = [p, h]
          addPoint (h1:h2:t) p
              | crossProduct h2 h1 p > 0 = addPoint (h2:t) p
              | otherwise = p : h1 : h2 : t

-- Calculate the perimeter of the convex hull
convexHullPerimeter :: [Point] -> Double
convexHullPerimeter points = sum $ zipWith distance hull (tail hull ++ [head hull])
    where hull = convexHull points

-- Parse input and calculate convex hull perimeter
main :: IO ()
main = do
    n <- readLn :: IO Int
    points <- mapM (\_ -> fmap ((\[x, y] -> (x, y)) . map read . words) getLine) [1..n]
    let result = convexHullPerimeter points
    putStrLn $ show result