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: Wrong Answer)

n = gets.to_i
@h = gets.split.map(&:to_i)

@count = 0


def calc(s, e)
  p [s, e]
  return if @h[s..e].all?{|a| a == 0}
  min = @h[s..e].min
  (s..e).each{|i| @h[i] -= min}
  @count += min
  l = -1

  (s..e).each do |i|
    if (i == e)
      if (@h[e] != 0) && (l == -1)
        @count += @h[e]
      elsif @h[e] != 0
        calc(l, e)
      elsif l != -1
        calc(l, e - 1)
      end
    else
      if @h[i] == 0
        if l != -1
          calc(l, i - 1)
        end
        l = -1
      else
        l = l == -1 ? i : l
      end
    end
  end
end

calc(0, n - 1)

puts @count