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 Scala (2.11.7) (judge verdict: Accepted)

import scala.io.StdIn._
import scala.collection.mutable.{ArrayBuffer, PriorityQueue}
object Main extends App {
  val Array(n, m) = readLine.split(" ").map(_.toInt)
  val arbeits = Array.fill(100001)(new ArrayBuffer[Int]())
  for (i <- 1 to n) {
    val Array(a, b) = readLine.split(" ").map(_.toInt)
    arbeits(a) += b
  }

  def exec(day: Int, possible: PriorityQueue[Int], income: Int): Int = {
    if (day > m) income
    else {
       possible ++= arbeits(day)
      if (possible.isEmpty) {
        exec(day + 1, possible, income)
      } else {
        val a = possible.dequeue()
        exec(day + 1, possible, income + a)
      }
    }
  }

  println(exec(1, PriorityQueue[Int](), 0))
}