n,m=list(map(int,input().split(" ")))
a=[]
for i in range(m):
  a.append(int(input()))
dp=[float("inf") for i in range(n+1)]
dp[0]=1
if 1 in a:
  dp[1]=0
else:
  dp[1]=1
for i in range(2,n+1):
  if i in a:
    dp[i]=0
  else:
    dp[i]=dp[i-1]+dp[i-2]
print(dp[n])

