You are given an array of $n$ integers. You will perform $n-1$ operations on the array.

In one operation, you will choose two numbers $a$ and $b$ from the array, delete both of them from the array and add $|a - b|$ into the array.

Your task is to find a sequence of operations such that the last number remaining in the array is $0$ .

The first line has an integer $n$ : the length of the array.

The next line has $n$ integers $x_1, x_2,\dots, x_n$ : the contents of the array.

• $2 \le n \le 1000$
• $1 \le x_i \le 1000$

Print $n-1$ lines each containing two integers $a$ and $b$ : the numbers chosen in the operations. You can print any valid solution.

If no solution exists, print only $-1$ .