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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Text;
using System.Numerics;
using System.IO;

namespace SolutionCS
{
    class Program
    {
        class work : IComparable<work>
        {
            public long days;
            public long money;

            public int CompareTo(work e)
            {
                int a = -money.CompareTo(e.money);
                if ( a == 0)
                {
                    return -days.CompareTo(e.days);
                }
                return a;
            }
        }

        static void Main(string[] args)
        {
            string[] s = Console.ReadLine().Split(' ');
            int N = int.Parse(s[0]);
            int M = int.Parse(s[1]);

            List<work> lists = new List<work>();
            for (int i = 0; i < N; i++)
            {
                s = Console.ReadLine().Split(' ');
                work w = new work();
                w.days = long.Parse(s[0]);
                w.money = long.Parse(s[1]);

                lists.Add(w);
            }
            lists.Sort();

            long ans = 0;
            for (int i = M; i > 0; i--)
            {
                if (lists.Count == 0)
                {
                    break;
                }

                while (lists[0].days > i)
                {
                    lists.RemoveAt(0);
                    if (lists.Count == 0)
                    {
                        break;
                    }
                }

                if ( lists.Count == 0)
                {
                    break;
                }

                ans += lists[0].money;
                lists.RemoveAt(0);
            }

            Console.WriteLine(ans);
        }
    }
}