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.Diagnostics;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Text;

class Procon {
    static void Main (string[] agrs) {
        var N = Int ();
        var M = Int ();
        var list = L<Tuple<int, int>> ();
        for (int i = 0; i < N; i++) {
            list.Add (T<int, int> (Int (), Int ()));
        }

        var slist = list.OrderByDescending (v => v.Item2).ThenByDescending (v => v.Item1);
        long ans = 0;
        int cur = 0;
        foreach (var v in slist) {
            if (cur + v.Item1 <= M) {
                ans += v.Item2;
                cur++;
            }
        }
        Dbg (ans);
    }

    static Scanner cin = new Scanner ();
    const int M = 1000000007;
    static void Dbg (object a) => Console.WriteLine (a);
    static void Dbg (string a) => Console.WriteLine (a);
    static void Dbg<T> (IEnumerable<T> a) => Dbg (string.Join (" ", a));
    static void Dbg<T> (params object[] a) => Dbg (string.Join (" ", a));
    static void Dbgs<T> (IEnumerable<T> a) => Dbg (string.Join ("\n", a));
    static void Dbgs<T> (params object[] a) => Dbg (string.Join ("\n", a));
    static int Int () => cin.nextInt ();
    static long Long () => cin.nextLong ();
    static int[] Ints () => cin.arrayInt ();
    static long[] Longs () => cin.arrayLong ();
    static double Double () => cin.nextDouble ();
    static double[] Doubles () => cin.arrayDouble ();
    static string String () => cin.nextString ();
    static string[] Strings () => cin.arrayString ();
    static char[] Chars () => String ().ToCharArray ();
    static T Max<T> (params T[] a) => a.Max ();
    static T Min<T> (params T[] a) => a.Min ();
    static List<T> L<T> () => new List<T> ();
    static List<T> L<T> (T[] v) => new List<T> (v);
    static Dictionary<T, U> Map<T, U> () => new Dictionary<T, U> ();
    static bool Contains<T, U> (Dictionary<T, U> d, T k) => d.ContainsKey (k);
    static Dictionary<T, U>.KeyCollection Keys<T, U> (Dictionary<T, U> d) => d.Keys;
    static Dictionary<T, U>.ValueCollection Values<T, U> (Dictionary<T, U> d) => d.Values;
    static Tuple<T1, T2> T<T1, T2> (T1 t1, T2 t2) => Tuple.Create (t1, t2);
}

class Scanner {
    string[] s;
    int i;
    int max_i;

    public Scanner () {
        s = new string[0];
        max_i = 0;
        i = 0;
    }

    public string nextString () {
        if (i >= s.Length) {
            s = Console.ReadLine ().Split (' ');
            max_i = s.Length;
            i = 0;
            if (max_i == 0) {
                return "";
            }
            return s[i++];
        } else {
            return s[i++];
        }
    }

    public int nextInt () {
        return int.Parse (nextString ());
    }

    public long nextLong () {
        return long.Parse (nextString ());
    }

    public double nextDouble () {
        return double.Parse (nextString ());
    }

    public string[] arrayString () {
        return Console.ReadLine ().Split (' ');
    }

    public int[] arrayInt () {
        string[] str = Console.ReadLine ().Split (' ');
        int[] array = new int[str.Length];
        for (int i = 0; i < str.Length; i++) {
            array[i] = int.Parse (str[i]);
        }
        return array;
    }

    public long[] arrayLong () {
        string[] str = Console.ReadLine ().Split (' ');
        long[] array = new long[str.Length];
        for (int i = 0; i < str.Length; i++) {
            array[i] = long.Parse (str[i]);
        }
        return array;
    }

    public double[] arrayDouble () {
        string[] str = Console.ReadLine ().Split (' ');
        double[] array = new double[str.Length];
        for (int i = 0; i < str.Length; i++) {
            array[i] = double.Parse (str[i]);
        }
        return array;
    }
}