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;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] vs = Console.ReadLine().Split().Select(p => int.Parse(p)).ToArray();
            int N = vs[0];
            int M = vs[1];
            List<int[]> jobs = new List<int[]>();
            for (int i = 0; i < N; i++) {
                jobs.Add(Console.ReadLine().Split().Select(p => int.Parse(p)).ToArray());
            }
            jobs = jobs.OrderByDescending(p => p[1]).OrderBy(p => p[0]).ToList();
            long sum = 0;
            for (int i = 1; i <= M; i++) {
                int[] job = null;
                int max = 0;
                foreach (var tmp in jobs) {
                    if (tmp[0] <= i && max < tmp[1]) {
                        job = tmp;
                        max = tmp[1];
                    }
                    if (tmp[0] == i) {
                        break;
                    }
                }
                if (job != null) {
                    sum += job[1];
                    jobs.Remove(job);
                }
            }
            Console.WriteLine(sum);
        }
    }
}