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: Wrong Answer)



object Main extends App {

  val Array(n, m) = scala.io.StdIn.readLine.split(" ").map(_.toInt)
  val ab = (0 until n).map { _ =>
    val Array(aa, bb) = scala.io.StdIn.readLine.split(" ").map(_.toInt)
    (bb, aa)
  }.sorted.reverse

  var ans = 0
  var day = 0
  var i = 0

  while (day < m && i < n) {
    while (i < n && ab(i)._2 + day > m) {
      i += 1
    }

    if (i < n) {
      ans += ab(i)._1
    }
    day += 1
    i += 1
  }

  println(ans)
}