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

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    static int[] LList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => int.Parse(ReadLine())).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, x) = (c[0], c[1]);
        var s = NList;
        var a = new int[n];
        var sum = 0L;
        for (var i = 0; i < n; ++i)
        {
            a[i] = x - s[i];
            sum += a[i];
        }
        for (var i = 0; i < n; ++i) if (s[i] % 2 == 0)
        {
            if (sum + s[i] / 2 == x)
            {
                WriteLine(s[i] / 2);
                return;
            }
        }
    }
}