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.chomp.to_i
ary = gets.chomp.split.map(&:to_i)

# n = 100, h.length = 100だからとりあえずおーだーは木にしない
# 最初の０じゃない要素から０じゃない要素まで１引くを１とカウント
count = 0
while true
  if !(ary.find_index {|item| item != 0})
    puts count
    break
  end
  count += 1
  # 0-index
  first = ary.find_index {|item| item != 0}
  i = 0
  while true
    # p first
    # p i
    if ary[first+i] == nil
      # p "here"
      break
    elsif ary[first+i] == 0
      # p "there"
      break
    else
      ary[first+i] -= 1
    end
    i += 1
  end
  # p ary
end