import numpy as np

N, M = map(int, input().split())
stairs_exist = np.ones(N+1)

for c in range(M):
    stairs_exist[int(input())] = 0
    
steps = np.zeros(N+1)
steps[0] = 1
for i in range(N):
    for j in range(i+1, min(N+1, i+3)):
        if stairs_exist[j]:
            steps[j] += steps[i]
            
print(int(steps[-1]))