function Main(input) {
  input = input.split("\n")
  input = input[0].split(" ").map(n => parseInt(n, 10));
  const a = input[0];
  const b = input[1];
  const c = input[2];
  const d = input[3];

  const ans = Math.max(a*c, a*d, b*c, b*d);

  console.log(ans.toString())
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));