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

namespace benzinkut
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] inp = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int n = inp[0];
            int min = inp[1];
            int[] helyk = new int[n];
            int[] stonks = new int[n];
            int[] ovr = new int[n];
            for (int f = 0; f < n; f++)
            {
                inp = Console.ReadLine().Split().Select(int.Parse).ToArray();
                helyk[f] = inp[0];
                stonks[f] = inp[1];
            }
            int max = helyk[n - 1];
            int i = n - 1;
            while (helyk[i] > max - min)
            {
                ovr[i] = stonks[i];
                i--;
            }
            int locmax = 0;
            for (int f = i; f >= 0; f--)
            {
                for (int k = 1; k < n - f; k++)
                {
                    if (helyk[f + k] >= helyk[f] + min && ovr[f + k] > locmax)
                    {
                        locmax = ovr[f + k];
                    }
                }
                ovr[f] = locmax + stonks[f];
                locmax = 0;
            }
            Console.WriteLine(ovr.Max());
            Console.ReadLine();
        }
    }
}