import numpy as np
N, M = map(int, input().split())
if M == 1:
    A = int(input())
else:
    A = np.array([int(input()) for _ in range(M)], dtype = int)

MOD= 1000000007
dp = np.zeros(N, dtype = int)
dp[A - 1] = -1
if dp[0] == -1 and dp[1] == -1:
    pass
elif dp[0] == -1:
    dp[1] = 1
elif dp[1] == -1:
    dp[0] = 1
else:
    dp[0] = 1; dp[1] = 2;


# if N >= 3:
#     for n in range(2, N):
#         if dp[n] != -1:
#             dp[n] = (max(dp[n-1], 0) + max(dp[n-2], 0)) % MOD

print (dp[-1])
