module Main (main) where

import           Control.Monad

main :: IO ()
main = do
  pointCount <- read <$> getLine
  points     <- replicateM pointCount (fmap read . head . reads <$> getLine)
  print $   sum
        $   zipWith (\(x1, y1) (x2, y2) -> sqrt $ (x2 - x1) ** 2 + (y2 - y1) ** 2)
        <*> tail
        $   take (pointCount + 1)
        $   cycle points