using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    static long[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, k) = (c[0], c[1]);
        var map = NArr(n);
        var set = new HashSet<long>{ 0 };
        foreach (var coin in map)
        {
            set.Add(coin[0]);
            set.Add(coin[1] + 1);
        }
        var list = new List<long>(set);
        list.Sort();
        var dic = new Dictionary<long, int>();
        for (var i = 0; i < list.Count; ++i) dic[list[i]] = i;
        var cum = new int[list.Count];
        foreach (var coin in map)
        {
            ++cum[dic[coin[0]]];
            --cum[dic[coin[1] + 1]];
        }
        var rest = k;
        for (var i = 1; i + 1 < cum.Length; ++i)
        {
            cum[i] += cum[i - 1];
            var count = (list[i + 1] - list[i]) * cum[i];
            if (rest < count)
            {
                WriteLine(list[i] + (rest / cum[i]));
                return;
            }
            rest -= count;
        }
    }
}