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.chop.split.map(&:to_i)
ab = []
N.times {ab << gets.chop.split.map(&:to_i)}

#　同じ数値がbが2つあったらaがでかい方を優先的に選ぶため、x[0]でもソート
ab.sort_by!{ |x| [x[1],x[0]] }.reverse!

ans = []
rem_days = M


N.times do |i|

  if ab[i][0] <= rem_days
    ans << ab[i][1]
    rem_days -= 1
  end

  break if rem_days == 0
end

if ans.empty?
  p 0
else
  p ans.inject(:+)
end