using System;
using System.Collections.Generic;
using System.Linq;
using BitArray = System.Collections.BitArray;
using BigInteger = System.Numerics.BigInteger;

namespace AtCoderProject
{
    public class Program
    {
        public object Calc()
        {
            var line = consoleReader.Split.Int;
            var N = line[0];
            var M = line[1];
            var works = consoleReader.Repeat(N).SplitInt.Select(PartTimeWork.FromArray)
                .Where(w => w.days <= M)
                .OrderBy(w => w.days)
                .ToArray();

            var remaining = new SortedList<int, int>(Comparer<int>.Create((p1, p2) => p2 - p1));
            long pay = 0;
            var i = 0;

            for (int d = 1; d <= M; d++)
            {
                while (i < works.Length && works[i].days <= d)
                {
                    var p = works[i++].pay;
                    if (remaining.ContainsKey(p))
                        ++remaining[p];
                    else
                        remaining.Add(p, 1);
                }

                if (remaining.Count > 0)
                {
                    var first = remaining.First();
                    pay += first.Key;
                    if (first.Value > 1)
                        --remaining[first.Key];
                    else
                        remaining.RemoveAt(0);
                }
            }

            return pay;
        }
        struct PartTimeWork
        {
            public static PartTimeWork FromArray(int[] l) => new PartTimeWork
            {
                days = l[0],
                pay = l[1]
            };
            public override string ToString() => $"days:{days}, pay:{pay}";
            public int days;
            public int pay;
        }

        #region いつもの
        private readonly ConsoleReader consoleReader;
        public Program(ConsoleReader consoleReader) { this.consoleReader = consoleReader; }
        static void Main() => Console.WriteLine(new Program(new ConsoleReader()).Calc()); static string AllLines<T>(IEnumerable<T> source) => string.Join("\n", source);
        #endregion
    }

#pragma warning disable
    public class ConsoleReader { public class SplitLine { string[] splited; public SplitLine(string line) { splited = line.Split(); } public string[] String => splited.ToArray(); public int[] Int => splited.Select(int.Parse).ToArray(); public long[] Long => splited.Select(long.Parse).ToArray(); public ulong[] ULong => splited.Select(ulong.Parse).ToArray(); public double[] Double => splited.Select(double.Parse).ToArray(); } public class RepeatLine { ConsoleReader reader; int num; public RepeatLine(ConsoleReader reader, int num) { this.reader = reader; this.num = num; } public IEnumerable<string> String { get { for (int i = 0; i < num; i++) yield return reader.String; } } public IEnumerable<int> Int { get { for (int i = 0; i < num; i++) yield return reader.Int; } } public IEnumerable<long> Long { get { for (int i = 0; i < num; i++) yield return reader.Long; } } public IEnumerable<string[]> SplitString { get { for (int i = 0; i < num; i++) yield return reader.Split.String; } } public IEnumerable<int[]> SplitInt { get { for (int i = 0; i < num; i++) yield return reader.Split.Int; } } } public virtual string String => Console.ReadLine(); public int Int => int.Parse(String); public long Long => long.Parse(String); public ulong ULong => ulong.Parse(String); public double Double => double.Parse(String); public SplitLine Split => new SplitLine(String); public RepeatLine Repeat(int count) => new RepeatLine(this, count); }
}

Measured memory_bytes: 23228