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 Ruby (2.3.3) (judge verdict: Accepted)

N = gets.to_i
h_array = gets.split.map(&:to_i)
count = 0

N.downto(1){|diff_num|
  start_array = [*1..((h_array.length)-(diff_num-1))]

  start_array.each do |start|
    last_flag = false

    loop do
      (start..(start+(diff_num-1))).each do |seq|
        if h_array[seq-1] == 0
          last_flag = true
          break
        end
      end

      unless last_flag
        (start..(start+(diff_num-1))).each do |seq|
          h_array[seq-1] -= 1
        end

        count += 1
      end

      break if last_flag
    end
  end
}

puts count