Let's consider Euclid's algorithm for finding the greatest common divisor, where $t$ is a list:

function Euclid(a, b):
    if a < b:
        swap(a, b)

    if b == 0:
        return a

    r = reminder from dividing a by b
    if r > 0:
        append r to the back of t

    return Euclid(b, r)

There is an array $p$ of pairs of positive integers that are not greater than $m$. Initially, the list $t$ is empty. Then the function is run on each pair in $p$. After that the list $t$ is shuffled and given to you.

You have to find an array $p$ of any size not greater than $2 \cdot 10^4$ that produces the given list $t$, or tell that no such array exists.

The first line contains two integers $n$ and $m$ ($1 \le n \le 10^3$, $1 \le m \le 10^9$) — the length of the array $t$ and the constraint for integers in pairs.

The second line contains $n$ integers $t_1, t_2, \ldots, t_n$ ($1 \le t_i \le m$) — the elements of the array $t$.

• If the answer does not exist, output $-1$.
• If the answer exists, in the first line output $k$ ($1 \le k \le 2 \cdot 10^4$) — the size of your array $p$, i. e. the number of pairs in the answer.

  The $i$-th of the next $k$ lines should contain two integers $a_i$ and $b_i$ ($1 \le a_i, b_i \le m$) — the $i$-th pair in $p$.

If there are multiple valid answers you can output any of them.