using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;

using E = System.Linq.Enumerable;

internal partial class Solver {
    class Task {
        public int Id, A, B, Limit;
    }
    public void Run() {
        var n = ni();
        var m = ni();
        var tasks = new List<Task>();
        for (int i = 0; i < n; i++) {
            var task = new Task { A = ni(), B = ni(), Id = i };
            task.Limit = m - task.A;
            tasks.Add(task);
        }
        tasks.Sort((t1, t2) => -t1.Limit.CompareTo(t2.Limit));
        var qu = new PriorityQueue<Task>((t1, t2) => -t1.B.CompareTo(t2.B));
        long ans = 0;
        int cursor = 0;
        for (int i = m; i >= 0; i--) {
            while (cursor < n && i <= tasks[cursor].Limit) {
                qu.Enqueue(tasks[cursor++]);
            }

            while (qu.Any()) {
                var top = qu.Dequeue();
                ans += top.B;
                break;
            }
        }
        cout.WriteLine(ans);
    }
}

public class PriorityQueue<T> {
    private T[] array = new T[100];
    private int size = 0;
    private readonly Comparer<T> _comparer;

    public PriorityQueue() {
        _comparer = Comparer<T>.Default;
    }

    public PriorityQueue(Comparison<T> comp) {
        _comparer = Comparer<T>.Create(comp);
    }

    private void Swap(int a, int b) {
        var t = array[a];
        array[a] = array[b];
        array[b] = t;
    }

    private void Expand() {
        var newlist = new T[array.Length * 2];
        Array.Copy(array, newlist, array.Length);
        array = newlist;
    }

    public bool Any() {
        return size > 0;
    }

    public void Enqueue(T newValue) {
        if (size >= array.Length) {
            Expand();
        }
        array[size++] = newValue;
        int pos = size - 1;
        while (pos > 0) {
            int parent = (pos - 1) / 2;
            if (_comparer.Compare(array[parent], array[pos]) > 0) {
                Swap(parent, pos);
                pos = parent;
            } else {
                break;
            }
        }
    }

    public T Peek() {
        return array[0];
    }

    public T Dequeue() {
        var top = array[0];
        array[0] = array[--size];
        int pos = 0;
        while (pos * 2 + 1 < size) {
            int left = pos * 2 + 1;
            int right = left + 1;
            int next = left;
            if (right < size && _comparer.Compare(array[left], array[right]) > 0) {
                next = right;
            }

            if (_comparer.Compare(array[pos], array[next]) > 0) {
                Swap(next, pos);
                pos = next;
            } else {
                break;
            }
        }

        return top;
    }
};


// PREWRITEN CODE BEGINS FROM HERE
internal partial class Solver : Scanner {
    public static void Main(string[] args) {
#if LOCAL
        new Solver(Console.In, Console.Out).Run();
#else
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Solver(Console.In, Console.Out).Run();
        Console.Out.Flush();
#endif
    }

#pragma warning disable IDE0052
    private readonly TextReader cin;
    private readonly TextWriter cout;
#pragma warning restore IDE0052

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        cin = reader;
        cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

#pragma warning disable IDE1006
#pragma warning disable IDE0051
    private int ni() { return NextInt(); }
    private int[] ni(int n) { return NextIntArray(n); }
    private long nl() { return NextLong(); }
    private long[] nl(int n) { return NextLongArray(n); }
    private double nd() { return NextDouble(); }
    private double[] nd(int n) { return NextDoubleArray(n); }
    private string ns() { return Next(); }
    private string[] ns(int n) { return NextArray(n); }
#pragma warning restore IDE1006
#pragma warning restore IDE0051
}

internal static class LinqPadExtension {
    public static T Dump<T>(this T obj) {
#if LOCAL
        return LINQPad.Extensions.Dump(obj);
#else
        return obj;
#endif
    }
}

public class Scanner {
    private readonly TextReader Reader;
    private readonly Queue<string> TokenQueue = new Queue<string>();
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        Reader = reader;
    }

    public int NextInt() { return int.Parse(Next(), ci); }
    public long NextLong() { return long.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        string[] array = new string[size];
        for (int i = 0; i < size; i++) {
            array[i] = Next();
        }

        return array;
    }
    public int[] NextIntArray(int size) {
        int[] array = new int[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextInt();
        }

        return array;
    }

    public long[] NextLongArray(int size) {
        long[] array = new long[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextLong();
        }

        return array;
    }

    public double[] NextDoubleArray(int size) {
        double[] array = new double[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextDouble();
        }

        return array;
    }

    public string Next() {
        if (TokenQueue.Count == 0) {
            if (!StockTokens()) {
                throw new InvalidOperationException();
            }
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext() {
        if (TokenQueue.Count > 0) {
            return true;
        }

        return StockTokens();
    }

    private static readonly char[] _separator = new[] { ' ', '\t' };
    private bool StockTokens() {
        while (true) {
            string line = Reader.ReadLine();
            if (line == null) {
                return false;
            }

            string[] tokens = line.Split(_separator, StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) {
                continue;
            }

            foreach (string token in tokens) {
                TokenQueue.Enqueue(token);
            }

            return true;
        }
    }
}


Measured memory_bytes: 23116