n,m = map(int,input().split())
a = set([int(input()) for _ in range(m)])
dp = [0]*(n+1)
dp[1] = int(1 not in a)
for i in range(2,n+1):
  if i in a:
    continue
  dp[i] = dp[i-1] + dp[i-2]
print(dp[n])