Problem:
Score : 400 points

Problem Statement

There are N one-off jobs available. If you take the i-th job and complete it, you will earn the reward of B_i after A_i days from the day you do it.

You can take and complete at most one of these jobs in a day.

However, you cannot retake a job that you have already done.

Find the maximum total reward that you can earn no later than M days from today.

You can already start working today.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i \leq 10^5

1 \leq B_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N

Output

Print the maximum total reward that you can earn no later than M days from today.

Sample Input 1

3 4
4 3
4 1
2 2

Sample Output 1

5

You can earn the total reward of 5 by taking the jobs as follows:

Take and complete the first job today. You will earn the reward of 3 after four days from today.

Take and complete the third job tomorrow. You will earn the reward of 2 after two days from tomorrow, that is, after three days from today.

Sample Input 2

5 3
1 2
1 3
1 4
2 1
2 3

Sample Output 2

10

Sample Input 3

1 1
2 1

Sample Output 3

0

Solution in Ruby (2.3.3) (judge verdict: Wrong Answer)

N, M = gets.chomp.split(' ').map(&:to_i)

AB = []
N.times do |i|
  AB[i] = gets.chomp.split(' ').map(&:to_i)
end

group_by_reward = AB.group_by{|v|v[1]}


reward_day = {}
group_by_reward.each do |k, v|
  reward_day[k] = v.map{|m| m[0]}.sort.reverse
end

sorted_reward_day = Hash[reward_day.sort.reverse]

@working_day = Array.new(M, nil)
sorted_reward_day.each do |r, days|
  days.each do |day|

    target_idx = (day - 1)
    next if target_idx > M - 1

    # while(!@working_day[target_idx].nil?)
    #   break if target_idx >= (M - 1)
    #   target_idx += 1
    # end

    if(!@working_day[target_idx].nil?)
      next
    end
    @working_day[target_idx] = r

  end
end

@output = 0
@working_day.each do |v|
  next if v.nil?
  @output += v
end
print @output