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 Python (3.4.3) (judge verdict: Wrong Answer)

BASE =  1000000007

class Counter(object):
    def __init__(self):
        self.counter = []
    def append(self, elem):
        self.counter.append(elem)
    def getCount(self, idx):
        pass

if __name__ == '__main__':
    N, M = [int(i) for i in input().split()]
    not_available = set()
    for i in range(M):
        not_available.add(int(input()))
    x = 0
    y = 1
    predicted_next = 1
    available = {i + 1 for i in range(N)} - not_available
    for elem in available:
        if predicted_next + 2 <= elem:
            y = 0
            break
        elif predicted_next + 1 == elem:
            x = 0
            predicted_next = elem + 2
        else:
            z = x + y
            x = y
            y = z
            predicted_next = elem + 1
    print(y % BASE)