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
hs = gets.split(" ").map{|n|n.to_i}
ans = 0
cut_start = -1
cut_end = -1
while !hs.all?{|nn|nn == 0}
(0).upto(hs.size - 1) do|n|
  if cut_start == -1
    if(hs[n] > 0)
      cut_start = n;
    end
    if (n == hs.size-1)
    cut_end = n
    (cut_start..cut_end).each do|nn|
      hs[nn] -= 1
    end
    ans += 1
    cut_start = -1
    cut_end = -1
    break;
    end
    next
  end


  # もう水やりしなくていいor端まで来た
  if(hs[n] == 0)
    cut_end = n-1
    (cut_start..cut_end).each do|nn|
      hs[nn] -= 1
    end
    ans += 1
    cut_start = -1
    cut_end = -1
    break;
  end
  if (n == hs.size-1)
  cut_end = n
  (cut_start..cut_end).each do|nn|
    hs[nn] -= 1
  end
  ans += 1
  cut_start = -1
  cut_end = -1
  break;
  end

  
  if(hs[n] > 0)
    next
  end
end
end
puts ans.to_s