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 group(xs)
  if xs[0] == 0
    group xs[1..-1]
  elsif xs.size == 0
    []
  else
    g = []
    rest = []
    xs.size.times {|i|
      if xs[i] != 0
        g << xs[i]
      else
        rest = xs[i+1..-1]
        break
      end
    }
    [g] + group(rest)
  end
end

def sum(xs)
  if xs.size > 0
    xs.inject :+
  else
    0
  end
end

def solve(g)
  m = g.min
  gs = group(g.map{|x| x - m})
  m + sum(gs.map{|h| solve(h)})
end

_ = gets.to_i
xs = gets.split.map(&:to_i)
p sum(group(xs).map{|g| solve(g)})