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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php

fscanf(STDIN, "%d %d", $n, $m);

$array = [];

$start = 0;
$sum = [];
for ($i = 1; $i <= $m; $i++) {
    $temp = 1;
    $tempb = 1;
    fscanf(STDIN, "%d", $array[$i]);
    if( $i != 1 && $array[$i] -1 == $array[$i-1]){
        echo 0;
        exit;
    }
    if($i != 1){

        $start = $array[$i-1] + 1;
    }else{
        $start = 0;
    }
    $stop = $array[$i] - 1;
    if($start == $stop){
        $sum[] = 1;
    }elseif($start + 1 == $stop ){
        $sum[] = 1;
    }else{
        for($j = 1; $j < ($stop - $start); $j++){
            $tempc = $tempb;
            $tempb = $temp;
            $temp = $temp + $tempc;
            if($temp > 1000000007){
                $temp = $temp %1000000007;
            }

        }
        $sum[] = $temp;
    }


}
$start = $array[$m] + 1;
$stop = $n;
$tempc = 1;
$temp = 1;
$tempb = 1;
if($start == $stop){
    $sum[] = 1;
}elseif($start + 1 == $stop ){
    $sum[] = 1;
}else{
    for($j = 1; $j < ($stop - $start); $j++){
        $tempc = $tempb;
        $tempb = $temp;
        $temp = $temp + $tempc;
        if($temp > 1000000007){
            $temp = $temp %1000000007;
        }

    }
    $sum[] = $temp;
}

$ans = 1;
foreach($sum as $value){
    $ans = $ans * $value;
    if($ans > 1000000007){
        $ans = $ans % 1000000007;
    }
}
echo ($ans % 1000000007);