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 = [0 for _ in range(N+1)]
dp[0] = 1
dp[1] = 1
for i in range(2, N+1):
  if B[i] != 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

if dp[-1] == -1:
  print(0)
else:
  print(dp[-1])