N, M = map(int, input().split())
aset = set([int(input()) for _ in range(M)])
dp = [0] * (N + 1)
dp[0] = 1
if 1 not in aset:
    dp[1] = 1
for i in range(2, N + 1):
    if i in aset:
        dp[i] = 0
    else:
        dp[i] = dp[i - 1] + dp[i - 2]
print(dp[-1])
