#nullable enable

using System.Numerics;

void Run()
{
    var n = Int();
    var m = Int();
    var a0 = 0L;
    var cards = new List<(int, int)>();
    for (var i = 0; i < n; i++)
    {
        var c = Int();
        var d = Int();
        if (c == 0)
        {
            a0 += d;
        }
        else
        {
            cards.Add((c, d));
        }
    }
    n = cards.Count;
    cards.Sort();
    cards.Reverse();
    var min = long.MinValue / 8;
    var f = new long[m + 1];
    for (var i = 0; i <= m; i++) f[i] = min;
    f[m] = 0;
    var ans = 0L;
    for (var y = 0; y < n; y++)
    {
        var g = new long[m + 1];
        for (var i = 0; i <= m; i++) g[i] = min;
        var (c, d) = cards[y];
        for (var x = 0; x <= m; x++)
        {
            var v = f[x];
            g[x] = Math.Max(g[x], v);
            var nx = (x - c) >> 1;
            if (nx >= 0) g[nx] = Math.Max(g[nx], v + d);
        }
        f = g;
    }
    for (var x = 0; x <= m; x++) ans = Math.Max(ans, f[x]);
    Out(ans + a0);
}

#region
AtCoderIO _io_;
var _backend_ = new StandardIOBackend();
_io_ = new(){ Backend = _backend_ };
Run();
_backend_.Flush();

string String() => _io_.Next();
int Int() => int.Parse(String());
void Out(object? x, string? sep = null) => _io_.Out(x, sep);

class AtCoderIO
{
    public required StandardIOBackend Backend { get; init; }

    Memory<string> _input = Array.Empty<string>();
    int _iter = 0;
    public string Next()
    {
        while (_iter >= _input.Length) (_input, _iter) = (Backend.ReadLine().Split(' '), 0);
        return _input.Span[_iter++];
    }

    public void Out(object? x, string? separator = null)
    {
        if (x == null) return;
        separator ??= Environment.NewLine;
        if (x is System.Collections.IEnumerable a and not string)
        {
            var objects = a.Cast<object>();
            if (separator == Environment.NewLine && !objects.Any()) return;
            x = string.Join(separator, objects);
        }
        Backend.WriteLine(x);
    }
}

class StandardIOBackend
{
    readonly StreamReader _sr = new(Console.OpenStandardInput());
    readonly StreamWriter _sw = new(Console.OpenStandardOutput()) { AutoFlush = false };
    public string ReadLine() => _sr.ReadLine()!;
    public void WriteLine(object? value) => _sw.WriteLine(value);
    public void Flush() => _sw.Flush();
}
#endregion

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}