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.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            //int[] inputNM = Console.ReadLine().Split().Select(int.Parse).ToArray();
            //int N = inputNM[0];
            //int M = inputNM[1];
            //List<int[]> input = new List<int[]>();
            //for (int i = 0; i < N; i++)
            //{
            //    input.Add(Console.ReadLine().Split().Select(int.Parse).ToArray());
            //}
            int N = 5;
            int M = 3;
            List<int[]> input = new List<int[]>();
            input.Add(new int[] { 1, 2 });
            input.Add(new int[] { 1, 3 });
            input.Add(new int[] { 1, 4 });
            input.Add(new int[] { 2, 1 });
            input.Add(new int[] { 2, 3 });
            int day = 0;
            int result = 0;
            input = input.OrderByDescending(a => a[1]).ThenByDescending(a => a[0]).ToList();
            while(day <= M)
            {
                for(int i = 0; i < input.Count; i++)
                {
                    if(input[i][0] + day <= M)
                    {
                        result += input[i][1];
                        input.RemoveAt(i);
                        break;
                    }
                }

                day++;
            }

            //出力
            Console.WriteLine(result);
            Console.ReadLine();
        }
    }
}