using System.Linq;
using System;

public class Hello
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        getAns(n, a);
    }
    static void getAns(int n, int[] a)
    {
        var c = a[0];
        var gp1 = a.Sum();
        var gp2 = c;
        for (int i = 1; i <= n; i++)
            gp2 += i % 2 == 0 ? a[i] : -a[i];
        var ans2 = (gp1 + gp2) / 2 - c;
        var ans1 = (gp1 - gp2) / 2;
        if (ans2 == 0)
        {
            if (ans1 == 0) Console.WriteLine("0\n{0}", c);
            else Console.WriteLine("1\n{0} {1}", c, ans1);
        }
        else Console.WriteLine("2\n{0} {1} {2}", c, ans1, ans2);
    }
}