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: Time Limit Exceeded)

import           Control.Applicative
import           Control.Monad
import           Data.List
import           Text.Printf

minAfter::(Ord a)=>[a]->[a]
minAfter []     = []
minAfter [x]    = []
minAfter [x,y]  = [y]
minAfter (x:xs) = min (head xs) (head $ minAfter xs) : minAfter xs

minBefore::(Ord a)=>[a]->[a]
minBefore = reverse . minAfter . reverse

main = do
    n<- getLine
    a<- map (read::String->Int) <$> replicateM (read n) getLine
    print $ maximum $ zipWith (-) (tail a) (minBefore a)