N_M = list(map(int, input().split()))
N = N_M[0]
M = N_M[1]
for i in range(M):
    dis[i] = list(int(input()))

dp = [0 for i in range(N+2)]
dp[0] = 1
if 1 in dis:
    dp[1] = 0
else :
    dp[1] = 1

for i in range(N):
    if i+2 in dis:
        dp[i+2]=0
    else:
        if i in dis :
            dp[i+2]=dp[i+1]
        if i+1 in dis :
            dp[i+2]=dp[i]
        else :
            dp[i+2]=dp[i]+dp[i+1]

print(dp[N])