module Main where

import Control.Monad
import Control.Applicative
import Data.List

showingList :: [Int] -> String
showingList (x:[]) = show x
showingList (x:xs) = (show x) ++ " " ++ (showingList xs)

solve :: [Int] -> Int -> Int
solve [] t = 0
solve (x:xs) t = if x >= t then solve xs x else solve xs t + t - x

main :: IO ()
main = do
    n <- getLine
    a <- map read . words <$> getLine :: IO [Int]
    putStrLn $ show (solve a 0)
