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;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Contest
{
    class Program
    {
        class Help
        {
            public int Key { get; set; }
            public int Value { get; set; }
        }
        static void Main(string[] args)
        {
            var nm = Array.ConvertAll(Console.ReadLine().Split(), Convert.ToInt32);
            int n = nm[0], m = nm[1];
            List<Help> ls = new List<Help>();
            while (n-- > 0)
            {
                var ab = Array.ConvertAll(Console.ReadLine().Split(), Convert.ToInt32);
                ls.Add(new Help { Key = ab[0], Value = ab[1] });
            }
            var sol1 = ls.OrderByDescending(x => x.Key).ThenByDescending(x => x.Value).ToList();
            var sol2 = ls.OrderByDescending(x => x.Key).ThenByDescending(x => x.Value).ToList();
            int res1 = 0, res2 = 0;
            for (int i = 0; i < n; i++)
            {
                if (sol1[i].Key <= m)
                    res1 += sol1[i].Value;
                if (sol2[i].Key <= m)
                    res2 += sol2[i].Value;
                m--;
            }
            Console.WriteLine(Math.Max(res1,res2));
        }
    }
}