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: Time Limit Exceeded)

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

class Program
{
    public static void Main()
    {
        var nm = Console.ReadLine().Split(' ').Select(x => Int32.Parse(x)).ToArray();
        var N = nm[0];
        var M = nm[1];
        var list = new List<int[]>();
        for (int i=0;i<N;++i)
        {
            var ab = Console.ReadLine().Split(' ').Select(x => Int32.Parse(x)).ToArray();
            list.Add(new int[] { ab[0], ab[1] });
        }
        var ans = 0;
        for (int i=0;i<M;++i)
        {
            var a = list.Where(x => x[0] <= i + 1).OrderByDescending(x => x[1]);
            if (1 <= a.Count())
            {
                var an = a.First();
                list.Remove(an);
                ans += (an[1]);
            }
        }
        Console.WriteLine(ans);
    }
}