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.split.map(&:to_i)
work = []
N.times do |i|
  a,b = gets.split.map(&:to_i)
  work << [a,b]
end
work.sort!{|x,y| y[0] <=> x[0]}
work.sort!{|x,y| y[1] <=> x[1]}

ans = 0
i = M
target = 0
while i != 0
  #puts "i = #{i} work = #{work}"
  work.each_with_index{|w,j|
    a,b = w
    if a <= i
      ans += b
      # puts "a = #{a} b = #{b} i = #{i} ans = #{ans}"
      work.delete_at(j)
      break
    else
      work.delete_at(j)
      next
    end
  }
  i -= 1
end
puts ans