const Main = (input) => {
  const[A,B,C,D] = input.split(' ').map(Number);
  const numbers = [A * C, A * D, B * C, C * D];
 
  console.log(Math.max.apply(null, numbers));
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));
// Main(`-1000000000 0 -1000000000 0`);
