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.List
import System.IO

f :: (Int,Int) -> Int -> (Int,Int)
f (m,a) x =
  let m' = min m x
      a' = max a (x-m)
  in
    (m',a')

exec :: (Int,Int) -> IO (Int,Int)
exec (m,a)= do
  l <- getLine
  let i = read l :: Int
      o = (m,a) `seq` i `seq` f (m,a) i
  eof <- isEOF
  if eof
  then return o
  else exec o

main = do
  n <- getLine
  (_,o) <- exec (2000000000,-2000000000)
  print o