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