mod = 1000000007

N, M = map(int, input().split())
Broken_set = set([])
for _ in range(M):
    Broken_set.add(int(input()))
dp = [0]*(N+1)
dp[0] = 1
dp[1] = 1

for i in range(2, N+1):
    if i in Broken_set:
        pass
    else:
        dp[i] = dp[i-1] + dp[i-2]

print(dp[N])