import Control.Applicative
import Control.Monad
import Data.List
import Data.Array
import Data.Char

main = do
  n <- (read::String -> Int) <$> getLine
  maximums <- listArray (1, n - 1) . map (read::String -> Int) . words <$> getLine
  let ans = foldl (\acc i -> acc + (min (maximums ! i) (maximums ! (i - 1)))) (maximums ! 1) [2..(n - 1)]
  print $ ans + maximums ! (n - 1)

