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.Text;
using System.Linq;
using static System.Console;
using System.Threading.Tasks;
namespace AtCoder
{
    class SummerVacation
    {
        struct Albeit
        {
            public int span,reward;
            //public float Efficiency => reward / (float)span;
            public static Albeit operator+(Albeit a, Albeit b)
            {
                return new Albeit()
                {
                    span = a.span + b.span,
                    reward = a.reward + b.reward
                };
            }
            public static Albeit operator -(Albeit a, Albeit b)
            {
                return new Albeit()
                {
                    span = a.span - b.span,
                    reward = a.reward - b.reward
                };
            }
        }
        static void Main()
        {
            var nm = ReadLine().Split(' ');
            var numAlbeits = int.Parse(nm[0]);
            var totalSpan = int.Parse(nm[1])+1;
            var albeits = new Albeit[numAlbeits];
            for (int i = 0; i < albeits.Length; i++)
            {
                var input = ReadLine().Split(' ');
                albeits[i] = new Albeit()
                {
                    span = int.Parse(input[0]),
                    reward = int.Parse(input[1])
                };

            }
            var totalReward = 0;
            var remainingSpan = totalSpan;
            var minSpan = albeits.Min(albeit => albeit.span);
            while (remainingSpan >= minSpan)
            {
                totalReward+= albeits.Where(albeit => albeit.span <= remainingSpan).Max(albeit => albeit.reward);
                remainingSpan--;
            }
            WriteLine(totalReward);

        }
    }
}