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;

namespace ConsoleApp1 {
    public struct ABData {
        public int a;
        public int b;
    }
    class P137C {
        static void Main(string[] args)
        {
            string[] str = Console.ReadLine().Split(' ');
            int n = int.Parse(str[0]);
            int m = int.Parse(str[1]);

            ABData[] darray = new ABData[n];

            for (int i = 0; i < n; i++)
            {
                string[] s = Console.ReadLine().Split(' ');
                darray[i] = new ABData();
                darray[i].a = int.Parse(s[0]);
                darray[i].b = int.Parse(s[1]);
            }

            Array.Sort(darray, new ABComparer());
            List<ABData> dlist = new List<ABData>(darray);

            int rew = 0;
            for (int i = 1; i <= m; i++)
            {
                int target = -1;
                int maxv = 0;
                for (int k = 0; k < dlist.Count; k++)
                {
                    if (dlist[k].a > i) break;

                    if (maxv < dlist[k].b)
                    {
                        maxv = dlist[k].b;
                        target = k;
                    }
                }
                if (target < 0) continue;

                rew += maxv;
                dlist.RemoveAt(target);
            }

            System.Console.WriteLine(rew);
        }
    }

    class ABComparer : IComparer<ABData> {
        public int Compare(ABData x, ABData y)
        {
            int diff = x.a - y.a;
            if (diff != 0)
            {
                return diff;
            }
            diff = y.b - x.b;
            return diff;
        }
    }


}