N,M = [int(i) for i in input().split()]
A = []
for _ in range(M):
    A.append(int(input()))
steps = [0]*N
for a in A:
    steps[a-1] = 1
cnt = []
for n in range(N):
    if n == 0:
        if steps[n]==0:
            cnt.append(1)
        elif steps[n]==1:
            cnt.append(0)
    elif n == 1:
        if steps[n]==0:
            cnt.append(cnt[n-1]+1)
        elif steps[n]==1:
            cnt.append(0)
    elif steps[n] == 0:
        cnt.append(cnt[n-2]+cnt[n-1])
    elif steps[n] == 1:
        cnt.append(0)
print(cnt[-1])