Problem:
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Maximum Profit

You can obtain profits from foreign exchange margin transactions. For example, if you buy 1000 dollar at a rate of 100 yen per dollar, and sell them at a rate of 108 yen per dollar, you can obtain (108 - 100) × 1000 = 8000 yen.

Write a program which reads values of a currency $R_t$ at a certain time $t$ ($t = 0, 1, 2, ... n-1$), and reports the maximum value of $R_j - R_i$ where $j > i$ .

Input

The first line contains an integer $n$. In the following $n$ lines, $R_t$ ($t = 0, 1, 2, ... n-1$) are given in order.

Output

Print the maximum value in a line.

Constraints

$2 \leq n \leq 200,000$

$1 \leq R_t \leq 10^9$

Sample Input 1

6
5
3
1
3
4
3

Sample Output 1

3

Sample Input 2

3
4
3
2

Sample Output 2

-1

Solution in Haskell (judge verdict: Accepted)

module Main where

import Control.Applicative
import Control.Monad
import Data.Function

data Stat = Stat Int Int

updateStat :: Stat -> Int -> Stat
updateStat (Stat smin sdiff) x =
    Stat newMin newDiff
    where
        newMin  = min x smin
        newDiff = if newMin == smin then max (x - newMin) sdiff else sdiff

initStat :: Int -> Int -> Stat
initStat x y =
    Stat smin sdiff
    where
        smin  = min x y
        sdiff = y - x

diffStat (Stat _ sdiff) = sdiff

max_diff (x:y:xs) =
    foldl updateStat (initStat x y) xs

main = do
    times <- (read <$> getLine) :: IO Int

    xs <- ($ times) . fix $ \loop n -> do
            if n /= 0 then do
                x  <- (read <$> getLine) :: IO Int
                xs <- loop (n-1)
                pure $ x : xs
            else pure []

    print $ diffStat $ max_diff xs