using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using static System.Console;
using static System.Math;

namespace Atcoder
{
    class Program
    {
        static StreamWriter sw = new StreamWriter(OpenStandardOutput()) { AutoFlush = false };
        static void Main(string[] args)
        {
            try
            {
                SetOut(sw);
                Solve.Answer();
                Out.Flush();
            }
            catch (Exception ex)
            {
                WriteLine(ex.ToString());
            }
        }
    }

    public class Solve
    {
        public static void Answer()
        {
            var n = IO.RInt;
            var a = IO.RSInt;
            var map = new int[n];
            for (int i = 0; i < n; i++)
            {
                map[a[i]]++;
            }
            long ans = pow(n);
            if (n % 2 == 0)
            {
                for (int i = 1; i < n; i += 2)
                {
                    if (map[i] != 2)
                    {
                        WriteLine(0);
                        return;
                    }
                }
                WriteLine(ans);
            }
            else
            {
                for (int i = 0; i < n; i += 2)
                {
                    if (i == 0)
                    {
                        if (map[i] != 1)
                        {
                            WriteLine(0);
                            return;
                        }

                    }
                    else
                    {
                        if (map[i] != 2)
                        {
                            WriteLine(0);
                            return;
                        }
                    }
                }
                WriteLine(ans);
            }
        }
        public static long pow(int n)
        {
            int m = n / 2;
            long ans = 1;
            for (int i = 0; i < m; i++)
            {
                ans = Mod.Multi(ans, 2);
            }
            return ans;
        }
    }

    public class IO
    {
        #region Input
        public static int RInt => int.Parse(ReadLine());
        public static long RLong => long.Parse(ReadLine());
        public static double RDouble => double.Parse(ReadLine());

        public static string[] RSString => ReadLine().Split();
        public static int[] RSInt => ReadLine().Split().Select(s => int.Parse(s)).ToArray();
        public static long[] RSLong => ReadLine().Split().Select(s => long.Parse(s)).ToArray();
        public static double[] RSDouble => ReadLine().Split().Select(s => double.Parse(s)).ToArray();
        #endregion

        #region Output
        public static void OutJoinSpace<T>(IEnumerable<T> list) => WriteLine(string.Join(" ", list));
        public static void WriteLineYes_or_No(bool flag) => WriteLine(flag ? "Yes" : "No");
        public static void WriteLineYES_or_NO(bool flag) => WriteLine(flag ? "YES" : "NO");
        #endregion
    }

    public class Mod
    {
        #region
        private readonly static long M = 1000000007;

        public static long Add(long a, long b) => (a * b) % M;
        public static long Sub(long a, long b) => (a - b) % M >= 0 ? (a - b) % M : (a - b) % M + M;
        public static long Multi(long a, long b) => (a * b) % M;
        #endregion
    }
}

Measured memory_bytes: 36640