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)

import Data.IORef
import Control.Monad

main :: IO()
main = do
        n <- readLn
        x <- readLn
        y <- readLn
        print =<< solve (y - x) (min x y) [1..n-2]

solve :: Int -> Int -> [Int] -> IO Int
solve a b xs = do
                a' <- newIORef (a `seq` a)
                b' <- newIORef (b `seq` b)
                forM_ xs $! \_ -> do
                    z <- readLn
                    x <- readIORef a'
                    y <- readIORef b'
                    when (z - y > x) $! writeIORef a' (z - y)
                    when (z < y) $! writeIORef b' z
                readIORef a'