n,m=map(int, input().split())
a=[]
for i in  range(m):
    a.append(int(input()))
dp=[[0]*(n+1)]
dp[0]=1
for i in range(1,n+1):
    if i in a:
        continue
        x=dp[i-1]
        if i>1:
            dp[i]+=dp[i-2]
ans=dp[n]
print(ans)
