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: Time Limit Exceeded)

import java.util.PriorityQueue

fun main(args: Array<String>)
{
    val (n, m) = readNInts()
    val ptj = mutableListOf<Pair<Int, Int>>()
    for (i in 1..n)
    {
        val (a, b) = readNInts()
        if (a > m) continue
        ptj.add(Pair(a, -b))
    }

    var ans = 0L
    val q = PriorityQueue<Int>()
    for (i in 1..m)
    {
        val candidate = ptj.filter{ it.first == i }

        for (item in candidate)
        {
            q.offer(item.second)
        }

        if (!q.isEmpty())
        {
            ans += -q.poll().toLong()
        }
    }

    println(ans)
}

// Read N integers separated by " "
// Usage: val (a, b, c) = readNInts()
fun readNInts() = readLine()!!.split(" ").map(String::toInt)