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)

fun main(args: Array<String>) {
    val line = readLine()!!
    val N = line.split(" ")[0].toInt()
    val M = line.split(" ")[1].toInt()

    var array: Array<IntArray> = Array(N) { IntArray(2) }
    for (i in 0 until N) {
        val R = readLine()!!
        array[i][0] = R.split(" ")[0].toInt()
        array[i][1] = R.split(" ")[1].toInt()
    }

    var score = 0
    for (i in 1..M) {
        var a = 0
        var b = -1
        for (j in 0 until N) {
            if (array[j][0] <= i) {
                if (array[j][1] > a) {
                    a = array[j][1]
                    b = j
                }
            }
        }
        if(b >= 0) {
            score += array[b][1]
            array[b][1] = 0
        }
    }

    println(score)
}