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(&:to_i)
$ans = 0

def zero_partition(x)
    list = []
    tmp = []
    x.each{|num|
        if num != 0
            tmp.push(num)
        else
            list.push(tmp) if tmp != []
            tmp = []
        end
    }
    list.push(tmp) if tmp != []
    return list
end

def loop(hs)
    min = hs.min
    tmp = hs.map{|x| x - min}
    $ans = $ans + min
    target = zero_partition(tmp)
    if target != []
        target.each{|arr|
            loop(arr)
        }
    end
end
loop(hs)
puts $ans