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

function fibonacci($n) {
  $f0 = $f1 = 1;
  for ($i = 2; $i <= $n; $i++) {
    $tmp = $f1;
    $f1 = $f0 + $f1;
    $f0 = $tmp;
  }

  return $f1;
}

$stdin = fscanf(STDIN, "%d %d\n");
for ($i = 0; $i < $stdin[1]; $i++) {
  $array[] = trim(fgets(STDIN)) * 1;
  if ($i != 0 && $array[$i] - $array[$i - 1] == 1) {
    print(0);
    return;
  }
}
$array[] = $stdin[0] + 1;
for ($i = 0; $i < count($array); $i++) {
  if ($i == 0) {
    $f = $array[$i] - 1;
    $sum = fibonacci($f);
    continue;
  }

  $f = $array[$i] - $array[$i - 1] - 2;
  $sum *= fibonacci($f);
  $sum %= 1000000007;
}

print($sum);