There are n lights aligned in a row. These lights are numbered 1 to n from left to right. Initially some of the lights are switched on. Shaass wants to switch all the lights on. At each step he can switch a light on (this light should be switched off at that moment) if there's at least one adjacent light which is already switched on. 

He knows the initial state of lights and he's wondering how many different ways there exist to switch all the lights on. Please find the required number of ways modulo 1000000007 (109 + 7).

Input

The first line of the input contains two integers n and m where n is the number of lights in the sequence and m is the number of lights which are initially switched on, (1 ≤ n ≤ 1000, 1 ≤ m ≤ n). The second line contains m distinct integers, each between 1 to n inclusive, denoting the indices of lights which are initially switched on.

Output

In the only line of the output print the number of different possible ways to switch on all the lights modulo 1000000007 (109 + 7).

Examples

Input

3 1
1


Output

1


Input

4 2
1 4


Output

2


Input

11 2
4 8


Output

6720

import java.io.*;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;


// graph, dfs,bfs, get connected components,iscycle, isbipartite, dfs on trees



public class scratch_25 {
    static class Graph{

        public static class Vertex{
            HashMap<Integer,Integer> nb= new HashMap<>();     // for neighbours of each vertex
        }

        public static HashMap<Integer,Vertex> vt;   // for vertices(all)

        public Graph(){
            vt= new HashMap<>();
        }

        public static int numVer(){
            return vt.size();
        }

        public static boolean contVer(int ver){
            return vt.containsKey(ver);
        }

        public static void addVer(int ver){
            Vertex v= new Vertex();
            vt.put(ver,v);
        }






        public static void addEdge(int ver1, int ver2, int weight){
            if(!vt.containsKey(ver1) || !vt.containsKey(ver2)){
                return;
            }
            Vertex v1= vt.get(ver1);
            Vertex v2= vt.get(ver2);
            v1.nb.put(ver2,weight);                                 // if previously there is an edge, then this replaces that edge
            v2.nb.put(ver1,weight);
        }

        public static void delEdge(int ver1, int ver2){

            if(!vt.containsKey(ver1) || !vt.containsKey(ver2)){
                return;
            }
            vt.get(ver1).nb.remove(ver2);
            vt.get(ver2).nb.remove(ver1);
        }
        public static void delVer(int ver){
            if(!vt.containsKey(ver)){
                return;
            }
            Vertex v1= vt.get(ver);
            ArrayList<Integer> arr= new ArrayList<>(v1.nb.keySet());
            for (int i = 0; i <arr.size() ; i++) {
                int s= arr.get(i);
                vt.get(s).nb.remove(ver);
            }
            vt.remove(ver);
        }
        static boolean done[];
        static int parent[];
        static ArrayList<Integer>vals= new ArrayList<>();


        public static boolean isCycle(int i){
            Stack<Integer>stk= new Stack<>();

            stk.push(i);
            while(!stk.isEmpty()){
                int x= stk.pop();
                vals.add(x);
                //   System.out.print("current="+x+" stackinit="+stk);
                if(!done[x]){
                    done[x]=true;
                }
                else if(done[x] ){
                    return true;
                }

                ArrayList<Integer>ar= new ArrayList<>(vt.get(x).nb.keySet());
                for (int j = 0; j <ar.size() ; j++) {
                    if(parent[x]!=ar.get(j)){
                        parent[ar.get(j)]=x;
                        stk.push(ar.get(j));
                    }
                }
                // System.out.println(" stackfin="+stk);
            }
            return false;
        }
        static int[]level;
        static int[] curr;
        static int[] fin;

        public static void dfs(int src){
            done[src]=true;
            level[src]=0;
            Queue<Integer>q= new LinkedList<>();
            q.add(src);
            while(!q.isEmpty()){
                int x= q.poll();
                ArrayList<Integer>arr= new ArrayList<>(vt.get(x).nb.keySet());
                for (int i = 0; i <arr.size() ; i++) {
                    int v= arr.get(i);
                    if(!done[v]){
                        level[v]=level[x]+1;
                        done[v]=true;
                        q.offer(v);
                    }
                }
            }
        }
        static int oc[];
        static int ec[];


        public static void dfs1(int src){
            Queue<Integer>q= new LinkedList<>();
            q.add(src);
            done[src]= true;
            //    int count=0;
            while(!q.isEmpty()){

                int x= q.poll();
                //   System.out.println("x="+x);
                int even= ec[x];
                int odd= oc[x];
                if(level[x]%2==0){
                    int val= (curr[x]+even)%2;
                    if(val!=fin[x]){
                        //  System.out.println("bc");
                        even++;
                        vals.add(x);
                    }
                }
                else{
                    int val= (curr[x]+odd)%2;
                    if(val!=fin[x]){
                        //   System.out.println("bc");
                        odd++;
                        vals.add(x);
                    }

                }
                ArrayList<Integer>arr= new ArrayList<>(vt.get(x).nb.keySet());
                //   System.out.println(arr);
                for (int i = 0; i <arr.size() ; i++) {
                    int v= arr.get(i);
                    if(!done[v]){
                        done[v]=true;
                        oc[v]=odd;
                        ec[v]=even;
                        q.add(v);
                    }
                }
            }

        }

        static long popu[];
        static long happy[];
        static long count[]; // total people crossing that pos
        static long sum[]; // total sum of happy people including that.


        public static void bfs(int x){
            done[x]=true;
            long total= popu[x];
//            long smile= happy[x];
            ArrayList<Integer>nbrs= new ArrayList<>(vt.get(x).nb.keySet());
            for (int i = 0; i <nbrs.size() ; i++) {
                int r= nbrs.get(i);
                if(!done[r]){
                    bfs(r);
                    total+=count[r];
//                    smile+=sum[r];
                }
            }
            count[x]=total;
//            sum[x]=smile;
        }


        public static void bfs1(int x){
            done[x]=true;
//            long total= popu[x];
            long smile= 0;
            ArrayList<Integer>nbrs= new ArrayList<>(vt.get(x).nb.keySet());
            for (int i = 0; i <nbrs.size() ; i++) {
                int r= nbrs.get(i);
                if(!done[r]){
                    bfs1(r);
//                    total+=count[r];
                    smile+=happy[r];
                }
            }
//            count[x]=total;
            sum[x]=smile;
        }


    }




    static class Reader {
        static BufferedReader reader;
        static StringTokenizer tokenizer;

        /**
         * call this method to initialize reader for InputStream
         */
        static void init(InputStream input) {
            reader = new BufferedReader(
                    new InputStreamReader(input));
            tokenizer = new StringTokenizer("");
        }

        /**
         * get next word
         */
        static String next() throws IOException {
            while (!tokenizer.hasMoreTokens()) {
                //TODO add check for eof if necessary
                tokenizer = new StringTokenizer(
                        reader.readLine());
            }
            return tokenizer.nextToken();
        }

        static int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        static double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        static long nextLong() throws IOException {
            return Long.parseLong(next());
        }
    }


    static class Pair implements Comparable<Pair> {
        long x;
        long y;
        long z;

        public Pair(long x, long y,long z) {
            this.x = x;
            this.y = y;
            this.z=z;
        }


        @Override
        public String toString() {
            return x + " " + y;
        }

        @Override
        public int compareTo(Pair o) {
            if(this.x >o.x){
                return 1;
            }
            else if(this.x==o.x){
                return 0;
            }
            else{
                return -1;
            }
        }
    }
    static class Pair1 implements Comparable<Pair1> {
        double d1;
        double d2;


        public Pair1(double d1, double d2) {
            this.d1 = d1;
            this.d2 =d2;
//            this.z=z;
        }


        @Override
        public String toString() {
            return d1 + " " + d2;
        }

        @Override
        public int compareTo(Pair1 o) {
            if(this.d1 >o.d1){
                return 1;
            }
            else if(this.d1==o.d1){
                return 0;
            }
            else{
                return -1;
            }
        }
    }




    // After writing solution, quick scan for:
    //   array out of bounds
    //   special cases e.g. n=1?
    //
    // Big numbers arithmetic bugs:
    //   int overflow
    //   sorting, or taking max, or negative after MOD




    static long modInverse(long a, long m)
    {

                             return power(a, m - 2, m);

    }

    public static void main(String[] args)  throws IOException {
        Reader.init(System.in);
        BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
        long n= Reader.nextLong();
        long m= Reader.nextLong();
        long arr[]= new long[(int)m];
        long mod=(long)(1e9+7);
        for (int i = 0; i <m ; i++) {
            arr[i]= Reader.nextLong();
        }
        Arrays.sort(arr);
        ArrayList<Long>x= new ArrayList<>();
        x.add((long)1);
        ArrayList<Long>diffs= new ArrayList<>();
        ArrayList<Long>diffs1= new ArrayList<>();
        for (int i = 0; i <m-1 ; i++) {
            if(arr[i+1]>arr[i]+1){
                diffs1.add(arr[i+1]-arr[i]-1);
            }
        }
//        System.out.println("diffs1="+diffs1);



        for (int i = 0; i <m ; i++) {
            x.add(arr[i]);
        }
        x.add(n);

        for (int i = 0; i <x.size()-1 ; i++) {
            long x1= x.get(i);
            long x2= x.get(i+1);
            if(x1!=x2 && x2!=(x1+1)){
                diffs.add(x2-x1-1);
            }
        }

//        long ans=1;
        long ans=fact(n-m,mod);
//        System.out.println(arr[0]-1+" "+(n-arr[(int)m-1]));
        ans= (ans%mod*modInverse(fact(arr[0]-1,mod),mod)%mod)%mod;
        ans= (ans%mod*modInverse(fact(n-arr[(int)m-1],mod),mod)%mod)%mod;
        for (int i = 0; i <m-1 ; i++) {
            ans= (ans%mod*modInverse(fact(arr[i+1]-arr[i]-1,mod),mod)%mod)%mod;
        }
//        System.out.println("ans="+ans);
////        out.append(ans+"\n");











        for (int i = 0; i <diffs1.size() ; i++) {
            long h= diffs1.get(i);
            ans=(ans%mod*power(2,h-1,mod)%mod%mod);
        }
        out.append(ans+"\n");



out.flush();
out.close();


    }
public static long fact(long n, long mod){
        long ans=1;
        while(n>0){
            ans=(ans%mod*n%mod)%mod;
            n--;
        }
        return ans;


}



    public static int localMinUtil(int[] arr, int low,
                                   int high, int n)
    {


        // Find index of middle element
        int mid = low + (high - low) / 2;

        // Compare middle element with its neighbours
        // (if neighbours exist)
        if(mid == 0 || arr[mid - 1] > arr[mid] && mid == n - 1 ||
                arr[mid] < arr[mid + 1])
            return mid;

            // If middle element is not minima and its left
            // neighbour is smaller than it, then left half
            // must have a local minima.
        else if(mid > 0 && arr[mid - 1] < arr[mid])
            return localMinUtil(arr, low, mid - 1, n);

        // If middle element is not minima and its right
        // neighbour is smaller than it, then right half
        // must have a local minima.
        return localMinUtil(arr, mid + 1, high, n);
    }

    // A wrapper over recursive function localMinUtil()
    public static int localMin(int[] arr, int n)
    {
        return localMinUtil(arr, 0, n - 1, n);
    }








    public static String convert(String s,int n){
        if(s.length()==n){
            return s;
        }
        else{
            int x= s.length();
            int v=n-x;
            String str="";
            for (int i = 0; i <v ; i++) {
                str+='0';
            }
            str+=s;
            return str;

        }
    }
    public static int lower(int arr[],int key){
        int low = 0;
        int high = arr.length-1;
        while(low < high){
            int mid = low + (high - low)/2;
            if(arr[mid] >= key){
                high = mid;
            }
            else{
                low = mid+1;
            }
        }
        return low;
    }

    public static int upper(int arr[],int key){
        int low = 0;
        int high = arr.length-1;
        while(low < high){
            int mid = low + (high - low+1)/2;
            if(arr[mid] <= key){
                low = mid;
            }
            else{
                high = mid-1;
            }
        }
        return low;
    }





    static long modExp(long a, long b, long mod) {
        //System.out.println("a is " + a + " and b is " + b);
        if (a==1) return 1;
        long ans = 1;
        while (b!=0) {
            if (b%2==1) {
                ans = (ans*a)%mod;
            }
            a = (a*a)%mod;
            b/=2;
        }
        return ans;
    }


    public static long modmul(long a, long b, long mod) {
        return b == 0 ? 0 : ((modmul(a, b >> 1, mod) << 1) % mod + a * (b & 1)) % mod;
    }

    static long sum(long n){
        //   System.out.println("lol="+ (n*(n-1))/2);
        return (n*(n+1))/2;
    }






    public static ArrayList<Integer> Sieve(int n) {
        boolean arr[]= new boolean [n+1];
        Arrays.fill(arr,true);
        arr[0]=false;
        arr[1]=false;
        for (int i = 2; i*i <=n ; i++) {
            if(arr[i]){
                for (int j = 2; j <=n/i ; j++) {
                    int u= i*j;
                    arr[u]=false;
                }}
        }
        ArrayList<Integer> ans= new ArrayList<>();
        for (int i = 0; i <n+1 ; i++) {
            if(arr[i]){
                ans.add(i);
            }
        }
        return ans;
    }




    static long power( long x, long y, long p)
    {

        long res = 1;


        x = x % p;

        if (x == 0) return 0;

        while (y > 0)
        {

            if((y & 1)==1)
                res = (res * x) % p;


            y = y >> 1;
            x = (x * x) % p;
        }
        return res;
    }

    public static long ceil_div(long a, long b){
        return (a+b-1)/b;
    }

    static long gcd(long a, long b)
    {
        if (a == 0)
            return b;
        return gcd(b % a, a);
    }

    static long lcm(long a, long b)
    {
        return (a*b)/gcd(a, b);
    }

}