using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using static System.Console;

class Program
{
    static void Main(string[] args)
    {
        new Program().Calc();
    }

    Scanner cin;

    public Program() { }

    bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
    bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (b.CompareTo(a) < 0) { a = b; return true; } return false; }

    void Calc()
    {
        cin = new Scanner();

        int N = cin.nextInt();
        int M = cin.nextInt();

        int[] A = cin.ArrayInt(M);
        int[] breakStep = new int[N + 2];

        for (int i = 0; i < M; ++i)
        {
            breakStep[A[i]] = 1;
        }

        breakStep[N + 1] = 1;

        int mul = 0;
        bool flag = true;

        for (int i = 0; i < N; ++i)
        {
            if (breakStep[i] == 1) continue;

            if (breakStep[i + 1] == 0 && breakStep[i + 2] == 0)
            {
                ++mul;
            }

            if (breakStep[i + 1] != 0 && breakStep[i + 2] != 0)
            {
                flag = false;
                break;
            }

        }

        int ans = 0;

        if (flag)
        {
            Modulo modulo = new Modulo(1);

            ans = modulo.Pow(2, mul);
        }


        WriteLine(ans);
    }
}

class Modulo
{
    private const int M = 1000000007;
    private readonly int[] m_facs;
    public int Mul(int a, int b)
    {
        return (int)(Math.BigMul(a, b) % M);
    }
    public Modulo(int n)
    {
        m_facs = new int[n + 1];
        m_facs[0] = 1;
        for (int i = 1; i <= n; ++i)
        {
            m_facs[i] = Mul(m_facs[i - 1], i);
        }
    }
    public int Fac(int n)
    {
        return m_facs[n];
    }
    public int Pow(int a, int m)
    {
        switch (m)
        {
            case 0:
                return 1;
            case 1:
                return a;
            default:
                int p1 = Pow(a, m / 2);
                int p2 = Mul(p1, p1);
                return ((m % 2) == 0) ? p2 : Mul(p2, a);
        }
    }
    public int Div(int a, int b)
    {
        return Mul(a, Pow(b, M - 2));
    }
    public int Ncr(int n, int r)
    {
        if (n < r) { return 0; }
        if (n == r) { return 1; }
        int res = Fac(n);
        res = Div(res, Fac(r));
        res = Div(res, Fac(n - r));
        return res;
    }
}

public static class StringExtension
{
    public static char GetChar1(this string str, int indexOneBase)
    {
        return str[indexOneBase - 1];
    }
}

class Scanner
{
    string[] s;
    int i;

    char[] cs = new char[] { ' ' };

    public Scanner()
    {
        s = new string[0];
        i = 0;
    }

    public string next()
    {
        if (i < s.Length) return s[i++];
        string st = Console.ReadLine();
        while (st == "") st = Console.ReadLine();
        s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
        if (s.Length == 0) return next();
        i = 0;
        return s[i++];
    }

    public int nextInt()
    {
        return int.Parse(next());
    }
    public int[] ArrayInt(int N, int add = 0)
    {
        int[] Array = new int[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextInt() + add;
        }
        return Array;
    }

    public long nextLong()
    {
        return long.Parse(next());
    }

    public long[] ArrayLong(int N, long add = 0)
    {
        long[] Array = new long[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextLong() + add;
        }
        return Array;
    }

    public double nextDouble()
    {
        return double.Parse(next());
    }


    public double[] ArrayDouble(int N, double add = 0)
    {
        double[] Array = new double[N];
        for (int i = 0; i < N; i++)
        {
            Array[i] = nextDouble() + add;
        }
        return Array;
    }
}
