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)

def split_by_0(arr, ans = [])
	return ans if arr.empty?
	index = arr.index(0)
	return ans << arr if index.nil?
	ans << arr[0..index-1] if index != 0
	split_by_0(arr[index+1..-1], ans)
end

def calc(hs, i = 0)
	return i if hs.empty?
	split_by_0(hs).each do |h|
		while !h.include?(0)
			h = h.map{ |h| h - 1 }
			i += 1
		end
		i = calc(h, i)
	end
	i
end

def test
	n = gets.to_i
	hs = gets.split(" ").map(&:to_i)
	calc(hs)
end

p test