import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

n,m = map(int,input().split())
A = [int(input()) for _ in range(m)] #壊れた階段

pos = 0
count = 1
dp = [0] * (n+1)
dp[0] = 1

for i in range(N+1):
    if (i+1) in A and (i+2) in A:
        print(0)
        exit()
    if (i+1) not in A:
        dp[i+1] += dp[i]
    if (i+2) not in A:
        dp[i+2] += dp[i]

print(dp[n])