Problem:
Score : 200 points

Problem Statement

Given are integers a,b,c and d.
If x and y are integers and a \leq x \leq b and c\leq y \leq d hold, what is the maximum possible value of x \times y?

Constraints

-10^9 \leq a \leq b \leq 10^9

-10^9 \leq c \leq d \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

a b c d

Output

Print the answer.

Sample Input 1

1 2 1 1

Sample Output 1

2

If x = 1 and y = 1 then x \times y = 1.
If x = 2 and y = 1 then x \times y = 2.
Therefore, the answer is 2.

Sample Input 2

3 5 -4 -2

Sample Output 2

-6

The answer can be negative.

Sample Input 3

-1000000000 0 -1000000000 0

Sample Output 3

1000000000000000000

Solution in Kotlin (1.3.71) (judge verdict: Accepted)

import java.io.BufferedReader
import java.io.BufferedWriter

fun main() = Case().exec(::solve)
//fun main() = TestExecutor.assert(testCase) { Case(it.r, it.w).exec(::solve) }

/** https://atcoder.jp/contests/abc178/tasks/abc178_b **/
fun solve(case: Case) {
    val (a, b, c, d) = case.longList()
    case.println(listOf(a * c, a * d, b * c, b * d).max()!!.toString())
}

class Case(
    private val input: BufferedReader = System.`in`.bufferedReader(),
    private val out: BufferedWriter = System.out.bufferedWriter()
) {
    fun exec(fn: (Case) -> Unit) = input.use { out.use { execInThread(fn) } }
    private fun execInThread(fn: (Case) -> Unit) =
        Thread(null, { fn(this) }, "solve", 64 * 1024 * 1024)
            .apply { setUncaughtExceptionHandler { _, e -> e.printStackTrace(); kotlin.system.exitProcess(1) } }
            .apply { start() }.join()

    fun println(c: CharSequence?) = out.appendln(c)
    fun string(): String = input.readLine().trimEnd()
    fun long(): Long = input.readLine().toLong()
    fun intList(): List<Int> = input.readLine().split(" ").map { it.toInt() }
    fun longList(): List<Long> = input.readLine().split(" ").map { it.toLong() }
}