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: Runtime Error)

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;
public class Main{
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int N=sc.nextInt();
		int M=sc.nextInt();
		ArrayList<Work> works=new ArrayList<Work>();
		for(int i=0;i<N;i++) {
			int a=sc.nextInt();
			int b=sc.nextInt();
			works.add(new Work(a,b));
		}
		Collections.sort(works,new Comp());
		/*for(Work w:works) {
			System.out.println(w.a);
		}*/
		int reward=0;
		for(int i=1;i<=M;i++) {
			//ArrayList<Work> kouho=new ArrayList<Work>();
			Work max=new Work(0,0);
			for(int j=0;j<works.size();j++) {
				Work w=works.get(j);
				if(w.a<=i&&w.b>max.b) {
					max=w;
				}
				if(w.a>i) {
					break;
				}
			}
			if(works.contains(max)) {
				works.remove(max);
			}
			reward+=max.b;
			//System.out.println(reward+" "+max);
		}
		System.out.println(reward);
	}
}
class Work{
	int a;
	int b;
	Work(int _a,int _b){
		a=_a;
		b=_b;
	}
}
class Comp implements java.util.Comparator<Work>{
	public int compare(Work a,Work b) {
		if(a.a>b.a) {
			return 1;
		}else {
			return -1;
		}
	}
}