N,M = map(int,input().split())
a = [int(input()) for _ in range(M)]
dp = [0]*(N+1)
dp[0] = 1
if N == 1:
  print(1)
else:
  for i in range(1,N+1):
    if i in a:
      continue
    elif i==1:
      dp[i] = dp[i-1]
    else:
      dp[i] = dp[i-1]+dp[i-2]
  print(dp[N])
