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 (1.3.71) (judge verdict: Time Limit Exceeded)

import java.util.*
import kotlin.Comparator

fun main(args: Array<String>) {
    val (n, m) = readIntList()
    val job = mutableMapOf<Int, PriorityQueue<Int>>()

    repeat(n) {
        val (a, b) = readIntList()

        if (job[a].isNullOrEmpty()) {
            job[a] = PriorityQueue<Int>(Collections.reverseOrder())
        }
        job[a]!!.add(b)
    }

    var ans = 0
    for (i in 1..m) {
        var maxIndex = -1
        var max = 0
        for (j in i downTo 1) {
            if (job[j].isNullOrEmpty()) continue
            if (job[j]!!.peek()!! > max) {
                max = job[j]!!.max()!!
                maxIndex = j
            }
        }
        if (maxIndex == -1) continue

        ans += job[maxIndex]!!.poll()
    }
    println(ans)
}

// Tools
fun readString() = readLine()!!
fun readInt() = readLine()!!.toInt()
fun readLong() = readLine()!!.toLong()
fun readStringList() = readLine()!!.split(" ")
fun readIntList() = readLine()!!.split(" ").map(String::toInt)
fun readLongList() = readLine()!!.split(" ").map(String::toLong)