using System.Linq;
using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var X = int.Parse(line[1]);
        line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, long.Parse);
        getAns(n, X, a);
    }
    static void getAns(int n, int X, long[] a)
    {
        var asum = a.Sum();
        foreach (var x in a)
        {
            if (x % 2 == 0)
            {
                var w = asum - x / 2;
                if (w % (n - 1) == 0 && w / (n - 1) == X) { Console.WriteLine(x / 2); return; }
            }
        }
    }
}