N,M = map(int,input().split())
a = [int(input()) for _ in range(M)]

dp = [0]*(N+1)
dp[0]=1
if 1 not in a:dp[1] = 1

for i in range(2,N+1):
  if i in a: continue
  dp[i] =dp[i-1]+dp[i-2]

print(dp[-1])
