ans' m a [] = a
ans' m a (x:xs) = 
  let m' = min m x
      a' = max a (x-m)
  in
    ans' m' a' xs

ans x = 
    let (x0:x1:xs) = x
        init_max  = x1 - x0
    in
      ans' x0 init_max (x1:xs)

main = do
    n <- getLine
    c <- getContents
    let i = map read $ lines c :: [Int]
        o = ans i
    print o