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)

n,m = map(int,input().split())
a = []
a.append(0)
for i in range(m):
    b = int(input())
    b -= 1
    a.append(b)
a.append(n)
b = []
b.append(1)
b.append(2)

for i in range(n-2):
    c =b[i]
    d = b[i+1]
    e = c + d
    b.append(e)

c = []
c.append(b[a[1] - a[0]  - 1])
i = 1
while i <= m:
    if a[i + 1] - a[i] > 1:
        c.append(b[a[i + 1] - a[i]  - 3])
        i += 1
    else:
        c.append(0)
        break
#print(c)
d = c[0] 
i = 1
#print(d)
while i < len(c):
    d = d * c[i]
    i += 1
print(d % 1000000007)