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

namespace ConsoleApplication2
{
    class Program
    {
        public class work
        {
            public int housyu;
            public int kikan;
        }
        static void Main(string[] args)
        {
            //var exStdIn = new System.IO.StreamReader("stdin.txt");
            //System.Console.SetIn(exStdIn);

            string[] input = Console.ReadLine().Split(' ');
            int N = int.Parse(input[0]);
            int M = int.Parse(input[1]);

            work[] w = new work[N];

            for (int i = 0; i < N; i++)
            {
                input = Console.ReadLine().Split(' ');
                w[i] = new work();
                w[i].kikan = int.Parse(input[0]);
                w[i].housyu = int.Parse(input[1]);
            }

            sort(N,w);
            int fee = 0;
            int idx = 0;
            var c = new Func<work, work,int>(Compare);

            PriorityQueue<work> pq = new PriorityQueue<work>(999999,c);
            for (int i = 0; i <= M; i++)
            {
                //キューに入れる
                while (idx<N)
                {
                    if (w[idx].kikan <= i)
                    {
                        pq.Enqueue(w[idx]);
                        idx++;
                    }
                    else
                    {
                        break;
                    }
                }
                if (pq.count() > 0)
                {
                    //キューから取り出す
                    work ww = pq.Dequeue();
                    fee += ww.housyu;
                }

            }

            Console.WriteLine(fee);
        }
        static int Compare(work a,work b)
        {
            if (a.housyu < b.housyu)
            {
                return 1;
            }
            else
            {
                return -1;
            }
        }
        static void sort(int N, work[] w)
        {
            for (int i = 0; i < N - 1; i++)
            {
                for (int j = i + 1; j < N; j++)
                {
                    if (w[i].kikan > w[j].kikan)
                    {
                        work buf1 = w[j];
                        w[j] = w[i];
                        w[i] = buf1;
                    }

                }
            }
        }
    }
    class PriorityQueue<T>
    {
        private readonly List<T> m_list;
        private readonly Func<T, T, int> m_compare;
        private int m_count;
        public PriorityQueue(int capacity, Func<T, T, int> compare)
        {
            m_list = new List<T>(capacity);
            m_compare = compare;
            m_count = 0;
        }
        public int count()
        {
            return m_count;
        }
        private int Add(T value)
        {
            if (m_count == m_list.Count)
            {
                m_list.Add(value);
            }
            else
            {
                m_list[m_count] = value;
            }
            return m_count++;
        }
        private void Swap(int a, int b)
        {
            T tmp = m_list[a];
            m_list[a] = m_list[b];
            m_list[b] = tmp;
        }
        public void Enqueue(T value)
        {
            int c = Add(value);
            while (c > 0)
            {
                int p = (c - 1) / 2;
                if (m_compare(m_list[c], m_list[p]) < 0) { Swap(p, c); } else { break; }
                c = p;
            }
        }
        public T Dequeue()
        {
            T value = m_list[0];
            m_list[0] = m_list[--m_count];
            int p = 0;
            while (true)
            {
                int c1 = p * 2 + 1;
                int c2 = p * 2 + 2;
                if (c1 >= m_count) { break; }
                int c = (c2 >= m_count || m_compare(m_list[c1], m_list[c2]) < 0) ? c1 : c2;
                if (m_compare(m_list[c], m_list[p]) < 0) { Swap(p, c); } else { break; }
                p = c;
            }
            return value;
        }
    }
}
/*
namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            //var exStdIn = new System.IO.StreamReader("stdin.txt");
            //System.Console.SetIn(exStdIn);

            long N = long.Parse(Console.ReadLine());

            string[] s = new string[N];
            Dictionary<string,long> h = new Dictionary<string, long>();
            long hit = 0;
            for (long i = 0; i < N; i++)
            {
                s[i] = Console.ReadLine();
                s[i] = sort(s[i]);
                if (h.ContainsKey(s[i]))
                {
                    hit += h[s[i]];
                    h[s[i]] = h[s[i]] + 1; ;
                }
                else
                {
                    h.Add(s[i],1);
                }
            }
            Console.WriteLine(hit);
        }
        static string sort(string s)
        {
            string[] c= new string[10];
            for (int i = 0; i < 10; i++)
            {
                c[i] = s.Substring(i, 1);
            }
            StringComparer cmp = StringComparer.OrdinalIgnoreCase;
            Array.Sort(c, cmp);
            s = "";

            for (int i = 0; i < 10; i++)
            {
                s += c[i];
            }
            return s;
        }
    }
}
*/