n,m=map(int,input().split())
a=[int(input()) for i in range(m)]

dp=[0]*(n+1)
dp[0]=1
for i in range(m):
    dp[a[i]]=-1

for i in range(1,n+1):
    if dp[i]==-1:continue
    if dp[i-1]!=-1:
        dp[i]+=dp[i-1]
    if i>1 and dp[i-2]!=-1:
        dp[i]+=dp[i-2]
print(dp[-1])