### typicalstairs

### 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 ≤ N ≤ 10`^{5}
`0 ≤ M ≤ N-1`
`1 ≤ a`_{1} < a_{2} < `...` ` < a`_{M} ≤ 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`.