// Slower C++ solution:
#include <iostream>

#include <sstream>

#include <iomanip>

#include <cstdio>

#include <cstdlib>

#include <cmath>

#include <cctype>

#include <cstring>

#include <vector>

#include <list>

#include <queue>

#include <deque>

#include <stack>

#include <map>

#include <set>

#include <algorithm>

#include <iterator>

#include <bitset>

#include <ctime>

using namespace std;



#define FOR(i,a,b) for (int i = (a); i < (b); i++)

#define RFOR(i,b,a) for (int i = (b)-1; i >= (a); i--)

#define ITER(it,a) for (__typeof(a.begin()) it = a.begin(); it != a.end(); it++)

#define FILL(a,value) memset(a, value, sizeof(a))



#define SZ(a) (int)a.size()

#define ALL(a) a.begin(), a.end()

#define PB push_back

#define MP make_pair



typedef long long LL;

typedef vector<int> VI;

typedef pair<int, int> PII;



const double PI = acos(-1.0);

const int INF = 1000 * 1000 * 1000 + 7;

const LL LINF = INF * (LL) INF;



const int MAX = 3 * 1000 * 100 + 47;

const double EPS = 1e-8;

const int MOD = 1000 * 1000 * 1000 + 7;





int A[4][4] =

{

    {1, 0, 0, 1},

    {1, 1, 0, 1},

    {1, 0, 1, 1},

    {1, 1, 1, 2}

};



int B[4][4] =

{

    {1, 0, 0, 0},

    {1, 1, 0, 0},

    {1, 0, 1, 0},

    {1, 1, 1, 1}

};



struct vect

{

    int A[4];

    vect()

    {

        FILL(A, 0);

    }

};



struct matrix

{

    int A[4][4];

    

    matrix()

    {

        FILL(A, 0);

    }

    

    matrix operator*(const matrix &m) const

    {

        matrix M;

        FOR(i, 0, 4)

            FOR(j, 0, 4)

                FOR(k, 0, 4)

                    M.A[i][j] = (M.A[i][j] + A[i][k] * 1LL* m.A[k][j]) % MOD;

        return M;

    }

    vect operator * (const vect& v) const

    {

        vect V;

        FOR(i, 0, 4)

            FOR(j, 0, 4)

                V.A[i] = (V.A[i] + A[i][j] * 1LL * v.A[j]) % MOD;

        return V;

    }

};





matrix BP(matrix M, int n)

{

    matrix RES;

    FOR(i, 0, 4)RES.A[i][i] = 1;

    while(n)

    {

        if (n & 1)RES = RES * M;

        M = M * M;

        n >>=1;

    }

    return RES;

}



int X[MAX];



int main()

{

    matrix A, B;

    FOR(i, 0, 4)FOR(j, 0, 4)A.A[i][j] = ::A[i][j];

    FOR(i, 0, 4)FOR(j, 0, 4)B.A[i][j] = ::B[i][j];

    

    int n, m;

    scanf("%d%d", &n, &m);

    FOR(i, 0, m)

    scanf("%d", X + i);

    X[m++] = n;

    

    vect V;

    V.A[0] = 1;

    FOR(i, 0, m)

    {

        matrix M = BP(A, X[i] - (i ? X[i-1] : 0) - 1);

        V = (M * B) * V;

    }

    cout << V.A[3] << endl;

    

    

    

}

    

    


// Faster C++ solution for the same problem (measured speedup: 5.170757442647354x):
#include <cstdio>

#include <assert.h>



typedef long long LL;



const int MAXM = 1e5, MOD = 1e9 + 7;

int n, m;



inline int add ( int a, const int b ) { return ( a += b ) < MOD ? a : a - MOD; }

inline int mul ( LL a, const int b ) { return ( a *= b ) < MOD ? a : a % MOD; }



inline int rint () {

	int x = 0; char s = getchar ();

	for ( ; s < '0' || '9' < s; s = getchar () );

	for ( ; '0' <= s && s <= '9'; s = getchar () ) x = x * 10 + ( s ^ '0' );

	return x;

}



struct Matrix {

	int n, m, mat[3][3];

	Matrix (): n ( 0 ), m ( 0 ), mat {} {}

	Matrix ( const int tn, const int tm ): n ( tn ), m ( tm ), mat {} {}

	inline int* operator [] ( const int key ) { return mat[key]; }

	inline Matrix operator * ( Matrix t ) {

		assert ( m == t.n );

		Matrix ret ( n, t.m );

		for ( int i = 0; i < n; ++ i ) {

			for ( int k = 0; k < m; ++ k ) {

				for ( int j = 0; j < t.m; ++ j ) {

					ret[i][j] = add ( ret[i][j], mul ( mat[i][k], t[k][j] ) );

				}

			}

		}

		return ret;

	}

};



inline Matrix qkpow ( Matrix a, int b ) {

	Matrix ret ( a.n, a.m );

	for ( int i = 0; i < ret.n; ++ i ) ret[i][i] = 1;

	for ( ; b; a = a * a, b >>= 1 ) if ( b & 1 ) ret = ret * a;

	return ret;

}



Matrix I ( 3, 1 ), A ( 3, 3 ), B ( 3, 3 );



inline void init () {

	I[0][0] = 1;

	A[0][0] = 1;

	A[1][0] = 2, A[1][1] = 1;

	A[2][0] = A[2][1] = A[2][2] = 1;

	B = A, ++ B[0][0], ++ B[0][1], ++ B[0][2];

}



int main () {

	init ();

	n = rint (), m = rint ();

	int las = 0;

	for ( int i = 1, x; i <= m; ++ i ) {

		x = rint ();

		I = A * qkpow ( B, x - las - 1 ) * I;

		las = x;

	}

	

	I = A * qkpow ( B, n - las - 1 ) * I;

	printf ( "%d\n", I[2][0] );

	return 0;

}