Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

{-# OPTIONS_GHC -O2 -funbox-strict-fields #-}
import qualified Data.ByteString.Char8 as B
import           Data.Char             (isSpace)
import qualified Data.Vector.Unboxed   as V

main :: IO ()
main = do
  n <- readLn
  hs <- V.unfoldrN n parseInt <$> B.getLine
  print $ solve n hs

solve :: Int -> V.Vector Int -> Int
solve _ hs = solve' hs

solve' :: V.Vector Int -> Int
solve' hs
  | V.length hs == 0 = 0
  | otherwise  = h + solve' (V.take i hs') + solve' (V.drop (i + 1) hs')
  where
    i = V.minIndex hs
    h = hs V.! i
    hs' = V.map (subtract h) hs

parseInt :: B.ByteString -> Maybe (Int, B.ByteString)
parseInt = B.readInt . B.dropWhile isSpace