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)


update [] _ = Nothing
update (h:hs) (x:xs)
  | h == x = (x:) <$> update hs xs
  | h > x  = Just $ grow (h:hs) (x:xs)
  where
    grow [] _ = []
    grow (h:hs) (x:xs)
      | h == x = x:xs
      | h > x = (x + 1) : grow hs xs

solv hs = go hs (repeat 0) 0 where
  go hs xs i =
    case update hs xs of
      Nothing -> i
      Just updated -> go hs updated (succ i)

main = do
  getLine
  hs <- map read . words <$> getLine
  print $ solv hs