Problem:
Score : 300 points

Problem Statement

There is a staircase with N steps. Takahashi is now standing at the foot of the stairs, that is, on the 0-th step.
He can climb up one or two steps at a time.

However, the treads of the a_1-th, a_2-th, a_3-th, \ldots, a_M-th steps are broken, so it is dangerous to set foot on those steps.

How many are there to climb up to the top step, that is, the N-th step, without setting foot on the broken steps?
Find the count modulo 1\ 000\ 000\ 007.

Constraints

1 \leq N \leq 10^5

0 \leq M \leq N-1

1 \leq a_1 < a_2 < ... < a_M \leq N-1

Input

Input is given from Standard Input in the following format:

N M
a_1
a_2
.
.
.
a_M

Output

Print the number of ways to climb up the stairs under the condition, modulo 1\ 000\ 000\ 007.

Sample Input 1

6 1
3

Sample Output 1

4

There are four ways to climb up the stairs, as follows:

0 \to 1 \to 2 \to 4 \to 5 \to 6

0 \to 1 \to 2 \to 4 \to 6

0 \to 2 \to 4 \to 5 \to 6

0 \to 2 \to 4 \to 6

Sample Input 2

10 2
4
5

Sample Output 2

0

There may be no way to climb up the stairs without setting foot on the broken steps.

Sample Input 3

100 5
1
23
45
67
89

Sample Output 3

608200469

Be sure to print the count modulo 1\ 000\ 000\ 007.

Solution in PyPy3 (2.4.0) (judge verdict: Runtime Error)

# C
# Typical Stairs

N_M = input()

N = int(N_M.split(" ")[0])
M = int(N_M.split(" ")[1])

a = []

for i in range(M):

    a.append(int(input()))

#print(a)

stairs = [0] * (N + 1)

if 1 in a:

    stairs[1] = 0
    stairs[2] = 1

elif 2 in a:

    stairs[1] = 1
    stairs[2] = 0

elif 1 in a and 2 in a:

    stairs[1] = 0
    stairs[2] = 0

else:

    stairs[1] = 1
    stairs[2] = 2

for i in range(N + 1):
    
    if i in a:

        stairs[i] = 0
    
    elif i > 2:

        stairs[i] = int(stairs[i - 1] + stairs[i - 2])

    #print(stairs)

print(stairs[-1] % 1000000007)