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

dp = [0]*(N+1)
if 1 in a: continue
else: dp[1]=1

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