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;

namespace question4
{
    class mydata
    {
        public int money;
        public int day;
        public mydata()
        {
            money = 0;
            day = 0;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            string[] str = Console.ReadLine().Split(' ');
            int N = int.Parse(str[0]);
            int M = int.Parse(str[1]);

            int[] A = new int[N];
            int[] B = new int[N];
            mydata[] C = new mydata[N];
            int[] chosen = new int[N];
            for (int i = 0; i < N; i++)
            {
                string[] str2 = Console.ReadLine().Split(' ');
                A[i] = int.Parse(str2[0]);
                B[i] = int.Parse(str2[1]);
                C[i] = new mydata();
                C[i].money = B[i];
                C[i].day = A[i];

            }

            Array.Sort(C, (a,b) => b.money - a.money );


            int highest = 0;
            int highestpos = -1;
            for (int k = 0; k < M; k++)
            {
                highestpos = -1;
                highest = 0;
                int day = M - k - 1;//今日を +0 日としたとき、+day 日目を走査する
                for (int i = 0; i < N; i++)
                {
                    if (chosen[i] == 0) //まだそのジョブが選ばれていなければ、
                    {
                        //if (A[i] <= (k+1))

                        if (C[i].day <= (k + 1))
                            {//もちろんM日後までに報酬がもらえるのが条件    

                            //if (highest <= B[i])
                            if (highest <= C[i].money)
                                {
                                highest = C[i].money;
                                highestpos = i;
                                break;
                            }
                        }
                    }
                }//走査終わり
                if (highestpos !=-1) chosen[highestpos] = 1;//ジョブを奪う

            }
            int res = 0;
            for (int i = 0; i < N; i++)
            {
                //Console.WriteLine(chosen[i].ToString());
                if (chosen[i] == 1) res += C[i].money;
            }

            Console.WriteLine(res.ToString());

            }
    }
}