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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int m = in.nextInt();
		int ab[][] = new int[n][2];

		for ( int i = 0; i < n; i++ ) {
			ab[i][0] = in.nextInt();
			ab[i][1] = in.nextInt();
		}
		Arrays.sort(ab, (a, b) -> Integer.compare(a[0], b[0]));

		long earn = 0;

		for ( int i1 = 1; i1 <= m; i1++ ) {

			int todayE = 0;
			int idx = -1;
			for ( int i2 = 0; i2 < n; i2++ ) {
				if(ab[i2][0] <= m - i1 + 1 && ab[i2][1] > todayE) {
					todayE = ab[i2][1];
					idx = i2;
				}
			}
			
			if(idx != -1) {
				ab[idx][1] = -1;
			}
			
			earn += todayE;
		}

		System.out.println(earn);

		in.close();
	}
}