private fun readInt() = readLine()!!.toInt()

private fun readInts() = readLine()!!.split(' ').map { it.toLong() }

fun main() {
    val v = readInts()
    val a = v.take(2)
    val b = v.takeLast(2)
    val x = listOf(a[0]*b[0], a[0]*b[1], a[1]*b[0], a[1]*b[1])
    println(x.max()!!)
}