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