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 qualified Data.ByteString.Char8 as BC
import Data.IORef
import Control.Monad(when)
import Data.Foldable(for_)
import Data.Maybe(fromJust)

main :: IO()
main = BC.getContents >>= solve.map (fst.fromJust.BC.readInt).BC.lines >>= print

solve :: [Int] -> IO Int
solve (_:x:y:xs) = do
                a <- newIORef (y - x)
                b <- newIORef (min x y)
                for_ xs $ \z -> do
                    a' <- readIORef a
                    b' <- readIORef b
                    when (z - b' > a') $ writeIORef a (z - b')
                    when (z < b')      $ writeIORef b z
                readIORef a