const main = stdin => {
  const input = stdin.trim().split('\n')

  const [a, b, c, d] = input[0].split(' ').map(x => BigInt(x))

  let aMax = 0
  if (a * c > a * d) {
    aMax = a * c
  } else {
    aMax = a * d
  }

  let bMax = 0
  if (b * c > b * d) {
    bMax = b * c
  } else {
    bMax = b * d
  }

  if (aMax > bMax) {
    console.log(aMax.toString())
  } else {
    console.log(bMax.toString())
  }
}


// 標準入力
main(require("fs").readFileSync("/dev/stdin", "utf8"))
