import sys
#from scipy.special import comb
from scipy.misc import comb

N,M = list(map(int, input().split()))

A = [0]*M

for i in range(M):
    A[i] = int(input())

A.append(N+1)

total_combo = 1
NOW = 0
for a in A:
    if NOW == a:
        print(0)
        sys.exit()
    L = a-1-NOW
    combo = 0
    for i in range(L//2 +1):
        j = L - 2*i
        combo += comb(j+1, i, exact=True)
    total_combo *= combo
    NOW = a + 1
    
print(total_combo)
