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.io.*;
import java.util.*;
public class Main{
    public static void main(String[] args) throws IOException{
        MyReader r = new MyReader();        
        int N, M;
        {int[] a = r.ii(); N = a[0]; M = a[1];}
        int[][] work = new int[N][2];
        for(int i = 0; i < N; i++)
            work[i] = r.ii();
            
        Arrays.sort(work, (x, y) -> {
            int z = -x[1]+y[1];
            return z == 0 ? -x[0]+y[0] : z;
        });
        long prf = 0;
        for(int i = 0, j = 0; i < M && j < N; j++){
            if(i+work[j][0] <= M){
                prf += work[j][1];
                i++;
            }
        }
        println(prf);
    }
    static void print(Object o){
        System.out.print(o.toString());
    }
    static void println(Object o){
        System.out.println(o.toString());
    }
    static int Int(String s){
        return Integer.parseInt(s);
    }
    static long Long(String s){
        return Long.parseLong(s);
    }
    static class MyReader extends BufferedReader{
        MyReader(){
            super(new InputStreamReader(System.in));
        }
        String s() throws IOException{
            return readLine();
        }
        String[] ss() throws IOException{
            return s().split(" ");
        }
        int i() throws IOException{
            return Int(s());
        }
        int[] ii() throws IOException{
            String[] ss = ss();
            int size = ss.length;
            int[] ii = new int[size];
            for(int j = 0; j < size; j++) ii[j] = Integer.parseInt(ss[j]);
            return ii;
        }
        long l() throws IOException{
            return Long(s());
        }
        long[] ll() throws IOException{
            String[] ss = ss();
            int size = ss.length;
            long[] ll = new long[size];
            for(int j = 0; j < size; j++) ll[j] = Long.parseLong(ss[j]);            
            return ll;
        }
    }
}