import math
def cmb(n, r, mod, g1, g2):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

def main():
    N, M = map(int, input().split())
    A = [-1] + [int(input()) for i in range(M)] + [N + 1]

    mod = 10**7+7 #出力の制限
    N = 10**5
    g1 = [1, 1] # 元テーブル
    g2 = [1, 1] #逆元テーブル
    inverse = [0, 1] #逆元テーブル計算用テーブル
    for i in range( 2, N + 1 ):
        g1.append( ( g1[-1] * i ) % mod )
        inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
        g2.append( (g2[-1] * inverse[-1]) % mod )

    d = [0] * (len(A) - 1)
    for i in range(len(A) - 1):
        if A[i+1] - A[i] == 1:
            print(0)
            exit(0)
        d[i] = A[i+1] - 1 - (A[i] + 1)

    ans = 1
    for dd in d:
        if dd > 1:
            tmp = 0
            for j in range(dd//2 + 1):
                tmp += cmb(dd - j, j, mod, g1, g2)
            ans *= tmp

    print(ans % 1000000007)

if __name__ == '__main__':
    main()
