n,m=list(map(int,input().split(" ")))
a=[]
for i in range(m):
  a.append(int(input()))
dp=[float("inf") for i in range(n)]
dp[0]=0
if 1 in a:
  dp[1]=0
else:
  dp[1]=1
for i in range(2,n):
  if (i-1 not in a)and(i-2 not in a):
    dp[i]=dp[i-1]+dp[i-2]
  elif (i-1 not in a)and(i-2 in a):
    dp[i]=dp[i-1]
  elif (i-1 in a)and(i-2 not in a):
    dp[i]=dp[i-2]
  else:
    dp[i]=0
print(n)