 "use strict";

const main = arg => {
  const input = arg.trim();
 
  const [ a , b , c , d ] = (input.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'));  
