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: Time Limit Exceeded)

n,m = gets.chomp.split.map(&:to_i)
jobs = Hash.new{|h,k| h[k] = Hash.new{|p,q| p[q]=0 }}
while str = gets
  a,b = str.chomp.split.map(&:to_i)
  next if a > m
  jobs[a][b] += 1
end
ret = 0
(1..m).each{|i|
  tmp = 0
  max = 0
  (1..i).each{|j|
    mm = jobs[i-j+1].keys.max || -1
    if mm > max
      max = mm
      tmp = i-j+1
    end
    }
  ret += max
  if jobs[tmp][max] == 1
    jobs[tmp].delete(max)
  else
    jobs[tmp][max] -= 1
  end
  }
p ret
h = {}