Problem:
Score : 300 points

Problem Statement

N persons are standing in a row. The height of the i-th person from the front is A_i.

We want to have each person stand on a stool of some heights - at least zero - so that the following condition is satisfied for every person:

Condition: Nobody in front of the person is taller than the person. Here, the height of a person includes the stool.

Find the minimum total height of the stools needed to meet this goal.

Constraints

1 \leq N \leq 2\times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print the minimum total height of the stools needed to meet the goal.

Sample Input 1

5
2 1 5 4 3

Sample Output 1

4

If the persons stand on stools of heights 0, 1, 0, 1, and 2, respectively, their heights will be 2, 2, 5, 5, and 5, satisfying the condition.

We cannot meet the goal with a smaller total height of the stools.

Sample Input 2

5
3 3 3 3 3

Sample Output 2

0

Giving a stool of height 0 to everyone will work.

Solution in Ruby (2.7.1) (judge verdict: Runtime Error)

#people_num = gets.chomp.to_i
# 5
#array = gets.chomp.split(" ").map(&:to_i)
# array = [2, 1, 5, 4, 3]

line = readline.map(&:chomp)
people_num = line[0].to_i
array = line[1].split(" ").map(&:to_i)

# 最終的に追加しなればならない踏み台の合計の高さ
add_height = 0

(1..people_num - 1).each do |n|
    # 自分よりも前の身長だけを格納したローカル配列
    pre_with_me = []
    (0..n - 1).each {|num|
        pre_with_me << array[num]
    }

    # pre_with_meの状態
    # [2]
    # [2, 1]
    # [2, 1, 5]
    # [2, 1, 5, 4]

    # 自分より前にいるやつで一番身長でかいやつを格納する変数
    pre_max = pre_with_me.max 
    if array[n] < pre_max
        gap = pre_max - array[n]
        add_height += gap
    end
end


p add_height