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: Runtime Error)

N,M = map(int,input().split())
pre_a = -1
k = []
ef = True
for i in range(M):
    a = int(input())
    if (a-pre_a == 1):break
    k.append(a-pre_a-2)
    pre_a = a
else:
    ef = False
    k.append(N-a-1)
nk = sorted(k)
def org_fib(t):
    t1 = 1
    t2 = 2
    fib = 0
    if t == 1:
        return t1
    elif t == 2:
        return t2
    else:
        for _ in range(t-2):
            fib = t1+t2
            t1 = t2
            t2 = fib
    return fib

if ef:print(0)
else:
    g = 1
    for nnkk in nk:
        if nnkk == 0:
            pass
        else:
            g = (g * org_fib(nnkk)) % 1000000007
    print(g)