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
fscanf(STDIN, "%d %d", $n, $m);
$a = array();
for($i=0;$i<$m;$i++){
  fscanf(STDIN, "%d", $a[$i]);
}
$count = 0;
$Fibonacci = [1, 1];
$count_array = array();
$number = 0;

for($k=0; $k<$m-1;$k++){
  if($a[$k] + 1 === $a[$k+1]){
    echo 0;
    return;
  }
}

for($j=2;$j<$n-1;$j++){
  $Fibonacci[$j] = $Fibonacci[$j-1] + $Fibonacci[$j-2];
}

for($p=0; $p<=$m;$p++){
  if($p == 0){
    if($a[$p] == 1){
      $number = 0;
    }
    else{
      $number = $a[$p] - 1;
    }
    $count_array[$p] = $Fibonacci[$number];
  }
  else if($p == $m){
    $number = $n - $a[$p-1] - 1;
    $count_array[$p] = $Fibonacci[$number];
  }
  else{
   	$number = $a[$p] - $a[$p-1] - 2;
    $count_array[$p] = $Fibonacci[$number];
  }
}

$count = array_product($count_array);
$answer = $count % 1000000007;

print_r($answer);
?>