function Main(input) {
  const [a, b, c, d] = input.split(" ").map(x => BigInt(x));
   
  let result = a * c;

  if (a * d) result = a * d;
  if (b * c) result = b * c;
  if (b * d) result = b * d;

  console.log(result.toString());
}

// Main(require("fs").readFileSync("sample.txt", "utf8"));  // テスト用
Main(require("fs").readFileSync("/dev/stdin", "utf8"));   // 提出用