"use strict";
const main = arg => {
  const input = arg.trim().split("\n");

  const [a,b,c,d] = parseInt(input[0].split(" "));//分割代入
  let ary = [];
  ary.push(a*c);
  ary.push(a*d);
  ary.push(b*c);
  ary.push(b*d);
  let res = Math.max(...ary);
  console.log(res);
  
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));  