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 OCaml (4.02.3) (judge verdict: Accepted)

let rec f hs =
    let (_, l) = Array.fold_left (fun (st, cnt) h ->
        h > 0, if h > 0 && not st then cnt + 1 else cnt)
        (false, 0)
        hs in
    if l > 0
    then l + f (Array.map (fun n -> n - 1) hs)
    else l

let id x = x

let () = Scanf.scanf "%d\n" @@ fun n ->
    Array.init n (fun _ -> Scanf.scanf " %d" id)
    |> f |> Printf.printf "%d\n"