n, m = map(int,input().split())
a = [int(input()) for i in range(m)]
dp = [0] * (n+1)
dp[0] = 1
dp[1] = 1
for i in a:
    dp[i] = 0
for i in range(2, n+1):
    if i not in a:
        dp[i] = dp[i-1] + dp[i-2]
print(dp[n])