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: Wrong Answer)

import Data.List (partition)

main :: IO ()
main = do
  getLine
  hs <- map (read :: String -> Int) . words <$> getLine
  print (f hs)

f :: [Int] -> Int
f [] = 0
f xs
  =
    let
        m = minimum xs
        xss = splits (fmap (subtract m) xs)
      in
        m + sum (fmap f xss)

splits :: [Int] -> [[Int]]
splits [] = []
splits xs
  =
    let
        (px, sx) = partition (> 0) xs
        sx' = dropWhile (== 0) sx
      in
        if null px then splits sx' else px : splits sx'