import java.util.*

fun main(args: Array<String>) {
  val sc = Scanner(System.`in`)
  val a = sc.nextLong()
  val b = sc.nextLong()
  val c = sc.nextLong()
  val d = sc.nextLong()

  val list = mutableListOf<Long>()
  list.add(a * c)
  list.add(a * d)
  list.add(b * c)
  list.add(b * d)

  println(list.max()!!)

}
