function Main(arg) {
  let a = Number(arg.trim().split(' ')[0]);
  let b = Number(arg.trim().split(' ')[1]);
  let c = Number(arg.trim().split(' ')[2]);
  let d = Number(arg.trim().split(' ')[3]);
  let list = [a*c, a*d, b*c, b*d];

  if(a < 0 && 0 < b){
    list.push(0);
  }
  if(c < 0 && 0 < d){
    list.push(0);
  }
  console.log(Math.max(...list));
}

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