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.STRef
import Control.Monad
import Control.Monad.ST
 
main :: IO()
main = getLine >> getContents >>= print.(\(x:y:xs) -> solve (y - x) (min x y) xs).map read.lines
 
solve :: Int -> Int -> [Int] -> Int
solve a b xs = runST $ do
                a' <- newSTRef a
                b' <- newSTRef b
                forM_ xs $ \z -> do
                    x <- readSTRef a'
                    y <- readSTRef b'
                    if (z - y > x) then writeSTRef a' (z - y) else return ()
                    if (z < y)     then writeSTRef b' z       else return ()
                readSTRef a'