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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
trim(fscanf(STDIN,"%d %d",$N,$M));
$a = -1;
$db = array();
$c =0;
if($c < $M){
        $a= trim(fgets(STDIN));
}
for($j = 0;$j<$N+1;$j++){
  echo $db[$j];
        if($j == $a){
                $db[$j] = 0;
                $c++;
                if($c < $M){
                $a= trim(fgets(STDIN));
                }
                }
        elseif($j == 0){
                $db[$j] = 1;
        }
        elseif($j == 1){
        $db[$j] = 1;
        }
        elseif($j > 1){

        $db[$j] = $db[$j-1] + $db[$j-2];
        }

}

echo $db[$N]%1000000007;
?>