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.*;
public class Main {
 public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
	int N=sc.nextInt();
	int[] M=new int[sc.nextInt()];
	Arrays.fill(M,0);
	
	String[] job=new String[10^4];
	Arrays.fill(job,"");//初期化せずに足していくとnull1,2,……となる？？？
	int tmp;
	for(int i=0;i<N;i++){
		tmp=sc.nextInt()-1;
		job[sc.nextInt()-1]+=tmp+",";//job[報酬]=日数,日数,日数……
	}
	int maxtmp=0;
	for(int i=10^4-1;i>0;i--)if(job[i]!="")job[i]=job[i].substring(0,job[i].length()-1);

	for(int i=10^4-1;i>0;i--){
		if(job[i]!=""){
			String[] st=job[i].split(",");
			for(String t:st){
				for(int j=Integer.valueOf(t).intValue();j>=0;j--){
					if(M[j]==0){
						M[j]=i+1;
						break;
					}
				}
			}
		}
	}
	int r=0;
	for(int i:M)r+=i;
	System.out.println(r);
 }
}