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: Runtime Error)

N, M = gets.split(' ').map(&:to_i)
works = Array.new(M + 1){Array.new}
N.times do |i|
	a, b = gets.split(' ').map(&:to_i)
	works[a].push(b)
end
1.upto(M) do |i|
	if !works[i].empty?
		works[i] = works[i].sort.reverse
	end
end

ans = 0
wl = []
1.upto(M) do |i|
	wl += works[i]
	if !wl.empty?
		n = wl.max
		ans += n
		t = wl.index(n)
		wl.delete_at(t)
	end
end

puts ans