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

def split(ary)
  s = []
  a = []
  ary.each do |e|
    if e == 0
      s.push(a) unless a.empty?
      a = []
    else
      a.push(e)
    end
  end
  s.push(a)
  s
end

def dfs(ary, sum)
  return 0 if ary.empty?
  return sum if ary.all? { |e| e == 0 }
  if ary.any? { |e| e == 0 }
    split(ary).map { |a| dfs(a, 0) }.inject(:+) + sum
  else
    water = ary.min
    ary = ary.map{ |e| e - water }
    sum += water
    dfs(ary, sum)
  end
end

puts dfs(h, 0)