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 = gets.split.map &:to_i

def rec(h)
	#p h
	if h.size == 1 then
		return h.first
	else
		# 最小値を持つ花で分割
		min = h.min

		i = 0
		new_hs = []
		ps = []
		while i < h.size do
			if h[i] != min then
				ps << h[i] - min
			elsif ps.size > 0 then
				new_hs << Marshal.load(Marshal.dump(ps))
				ps = []
			end
			i += 1
		end
		if ps.size > 0 then
			new_hs << Marshal.load(Marshal.dump(ps))
		end

		# 分割した全ての部分について水やり回数を合計
		#p "new_hs: #{new_hs}"
		result = new_hs.map{|n_h| rec(n_h)}
		#p "result: #{result}"
		return min + result.inject(0, :+)
	end
end

p rec(h)