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 function(ary)
    tmp = []
    sum = []
    ary.length.times do |i|
        if ary[i] != 0 then
            tmp << ary[i]
        else
            if tmp.length > 0 then
                sum << tmp
            end
            tmp = []
        end
        if i == ary.length - 1 && tmp.length != 0 then
            sum << tmp
        end
    end
    sum
end

N = gets.chomp.to_i
h = gets.split(' ')
h = h.map{|x| x.to_i}

f = 1
count = 0
while f == 1 do
    t = function(h)
    if t.length == 0 then
        f = 0
        break
    end
    count += t.length
    h = h.map do |x|
        if x > 0 then
            x - 1
        else
            0
        end
    end
end

print count