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 Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.PriorityQueue
import kotlin.comparisons.compareByDescending
fun main(arg: Array<String>) {
    val (N, M) = listOfInt()
    val jobs = Array(M) { mutableListOf<Int>() }
    repeat(N) {
        val (A, B) = listOfInt()
        if (A <= M) jobs[M - A].add(B)
    }
    var ans = 0L
    val q = PriorityQueue<Int>(N, compareByDescending { it })
    for (n in (0 until M).reversed()) {
        jobs[n].forEach { q.add(it) }
        if (q.size > 0) {
            ans += q.poll()!!
        }
    }
    println(ans)
}
fun next() = readLine()!!
fun listOfString() = next().split(" ")
fun listOfInt(delta: Int = 0) = listOfString().map { Integer.parseInt(it) + delta }