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_LIST = gets.split(' ').take(N).map(&:to_i)

# [[i, size], ...]
def mk_candidate_list(list)
  candidate_list = []
  i = 0
  while i < list.size
    l = list[i..-1].take_while.with_index do |h, j|
      h < H_LIST[i + j]
    end
    if l.size > 0
      candidate = [i, l.size]
      candidate_list.push(candidate)
    end
    i += l.size + 1
  end
  candidate_list
end

answer = 0
list = Array.new(N, 0)
candidate_list = mk_candidate_list(list)
while candidate_list.size > 0
  i, size = candidate_list.max_by { |i, size| size }
  list =
    list[0...i] + list[i, size].map(&:next) + list[(i + size)..-1]
  candidate_list = mk_candidate_list(list)
  answer += 1
end
puts answer