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 solve(n, hn, depth)
  return 0 if n == 0

  min = hn.min
  return min if n == 1

  (0..n-1).each { |i| hn[i] -= min}

  start = hn[0] == 0 ? 1 : 0
  i = start
  ans = min
  while i < n do
    if hn[i] == 0
      tmp = solve(i - start, hn[start..(i-1)], depth + 1)
      ans += tmp
      start = i + 1
    end

    i += 1
  end
  if hn[i-1] != 0
    ans += solve(i - start, hn[start..(i-1)], depth + 1)
  end

  ans
end

n = gets.to_i
hn = gets.split.map(&:to_i)

puts solve(n, hn, 0)