n, m = map(int, input().split())
alis = list(int(input()) for _ in range(m))
dp = [-1]*(n+1)
for i in alis:
    dp[i] = 0
dp[0] = 1
dp[1] = 1
for i in range(2,n+1):
    if dp[i] == -1:
        dp[i] = dp[i-1] + dp[i-2]
print(dp[n])