mod=10**9+7
N,M=map(int,input().split())
A=[int(input()) for m in range(M)]
L=[1 for n in range(N+1)]
for a in A:
    L[a]=0
Block=[0,1]
for n in range(1,N+1):
    if L[n]==1:
        Block=Block[1:]+[sum(Block)]
    else:
        Block=Block[1:]+[0]
print(Block[-1])