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;

namespace D
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] input = Console.ReadLine().Split().Select(i => Convert.ToInt32(i)).ToArray();
            int N = input[0];
            int M = input[1];
            List<Data> data = new List<Data>();
            for (var i = 0; i < N; i++)
            {
                input = Console.ReadLine().Split().Select(j => Convert.ToInt32(j)).ToArray();
                data.Add(new Data(input[0], input[1]));
            }
            data = data
                    .OrderByDescending(i => i.B)
                    .ThenByDescending(day => day.A)
                    .ToList();
            long max = 0L;
            int index = 0;
            for (var i = M; i >= 0; i--)
            {
                while (index < N)
                {
                    if (data[index].A <= i)
                    {
                        Console.WriteLine($"{data[index]} - 残り{i}日");
                        max += data[index].B;
                        index++;
                        break;
                    }
                    index++;
                }
                if (index >= N)
                    break;
            }
            Console.WriteLine(max);
        }
    }

    class Data
    {
        public int A;
        public int B;

        public Data(int a, int b)
        {
            A = a;
            B = b;
        }

        public override string ToString()
        {
            return $"{A} - {B}";
        }
    }
}