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)

s = list(map(int, input().split()))
n,m = s[0],s[1]
a = [int(input()) for i in range(m)]



if n == 1:
    print(1)

elif n == 2:
    if m == 0:print(2)
    elif m == 1:
        if a[0] == 2:print(0)
        else:print(1)
        
    
elif n == a[-1]-1:
    print(0)
    
else:
    if m == 0:
        t = -1
    else:
        c = 0
        t = a[c]-1
    x, y = 0, 1
    for i in range(n):
        if x == 0 and y == 0:
            break
        elif i == t:
            x, y = y, 0
            if a[c]-1 == a[-1]-1:
                continue
            else:
                c += 1
                t = a[c]-1
        else:
            x, y = y, x + y
    print(y%1000000007)