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: Runtime Error)

def calc(a)
  return 0 unless a
  return a[0] if a.length == 1
  return a.max if a.length == 2
  min = a.min
  a.map!{|i| i - min}
  next_list = []
  s = 0
  zero_index = [-1]  
  a.each_with_index do |num,i|
    zero_index << i if num == 0
  end
  zero_index << 0
  return min + (1..zero_index.length - 1).inject(0){|res,i| res += calc(a[zero_index[i - 1] + 1..zero_index[i] - 1])}
end
n = gets.to_i
a = gets.chomp.split(' ').map(&:to_i)
puts calc(a)