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
hs = gets.split(" ").map(&:to_i)

$count = 0

def foo(array)
  return if array.empty? || array.all?{|a| a == 0}
  tmp_array = Array.new([])
  i = 0
  array.each do |a|
    if a == 0
      i += 1
    else
      tmp_array[i] ||= []
      tmp_array[i] << a
    end
  end
  tmp_array.compact!
  $count += tmp_array.size
  tmp_array.each do |t|
    tmp = t.map{|e2| e2 - 1}
    foo(tmp)
  end
end

foo(hs)
puts $count