Problem:
Score : 500 points

Problem Statement

There are N integers, A_1, A_2, ..., A_N, written on a blackboard.

We will repeat the following operation N-1 times so that we have only one integer on the blackboard.

Choose two integers x and y on the blackboard and erase these two integers. Then, write a new integer x-y.

Find the maximum possible value of the final integer on the blackboard and a sequence of operations that maximizes the final integer.

Constraints

2 \leq N \leq 10^5

-10^4 \leq A_i \leq 10^4

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible value M of the final integer on the blackboard, and a sequence of operations x_i, y_i that maximizes the final integer, in the format below.

Here x_i and y_i represent the integers x and y chosen in the i-th operation, respectively.

If there are multiple sequences of operations that maximize the final integer, any of them will be accepted.

M
x_1 y_1
:
x_{N-1} y_{N-1}

Sample Input 1

3
1 -1 2

Sample Output 1

4
-1 1
2 -2

If we choose x = -1 and y = 1 in the first operation, the set of integers written on the blackboard becomes (-2, 2).

Then, if we choose x = 2 and y = -2 in the second operation, the set of integers written on the blackboard becomes (4).

In this case, we have 4 as the final integer. We cannot end with a greater integer, so the answer is 4.

Sample Input 2

3
1 1 1

Sample Output 2

1
1 1
1 0

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
	"sort"
	"fmt"
	"bufio"
	"os"
	"strconv"
)

//•*¨*•.¸¸♪I/O•*¨*•.¸¸♪

var (
	sc = bufio.NewScanner(os.Stdin)
	wr = bufio.NewWriter(os.Stdout)
)

func scanInt() int {
	sc.Scan()
	a,_ := strconv.Atoi(sc.Text())
	return a
}

func scanInt64() int64 {
	sc.Scan()
	a,_ := strconv.ParseInt(sc.Text(),10,64)
	return a
}

func scanFloat64() float64 {
	sc.Scan()
	a,_ := strconv.Atoi(sc.Text())
	return float64(a)
}

func scanInts(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ { res[i] = scanInt() }
	return res
}

func scanText() string {
	sc.Scan()
	return sc.Text()
}

func printInts(a ...int) {
	for i, e := range a {
		fmt.Fprint(wr, e)
		if i != len(a)-1 { fmt.Fprint(wr, " ") }
	}
	fmt.Fprintln(wr)
	wr.Flush()
}

//•*¨*•.¸¸♪Main•*¨*•.¸¸♪(　-ω-)ノ　(　・ω・)

func main() {
	sc.Split(bufio.ScanWords)
	// sc.Buffer(make([]byte, 10000), 100000000)

	n := scanInt()
	a := scanInts(n)

	x := make([]int, 0)
	y := make([]int, 0)
	
	sort.Ints(a)

	for i := 0; i < n-2; i++ {
		if a[i] < 0 {
			if a[i+1] > 0 {
				x = append(x,a[i])
				y = append(y,a[i+1])
				a[i+1] = a[i] - a[i+1]
			} else {
				x = append(x,a[n-1])
				y = append(y,a[i])
				a[n-1] -= a[i]
			}
		} else {
			x = append(x,a[i])
			y = append(y,a[i+1])
			a[i+1] = a[i] - a[i+1]
		}
	}

	x = append(x,a[n-1])
	y = append(y,a[n-2])
	a[n-1] -= a[n-2]

	fmt.Println(a[n-1])
	for i := 0; i < len(x); i++ {
		fmt.Println(x[i],y[i])
	}

}