function Main(input) {
  // input = input.trim().split("\n").map(function(x) { return x.split(" ")});
  // let a = BigInt(input[0][0], 10);
  // let b = BigInt(input[0][1], 10);
  // let c = BigInt(input[0][2], 10);
  // let d = BigInt(input[0][3], 10);

  const text = input.split(" ").map(x => +x);
  const a = text[0],
        b = text[1],
        c = text[2],
        d = text[3];

  let ans = a * c;
  if (ans < a * d) ans = a * d;
  if (ans < b * c) ans = b * c;
  if (ans < b * d) ans = b * d;
  console.log(ans.toString());

}

// Main(require("fs").readFileSync("sample.txt", "utf8"));
Main(require("fs").readFileSync("/dev/stdin", "utf8"));