n,m=map(int,input().split())
a=[0]*(n+1)
b=[int(input()) for i in range(m)]
a[0]=1
j=0
if b[0]==1:
  a[1]=0
  j=1
else:
  a[1]=1
for i in range(2,n+1):
  if i==b[j]:
    if j<m-1:
      j+=1
  else:
    a[i]=a[i-1]+a[i-2]
print(a[n])