'use script';

{
function Main(input) {
	tmp = input.split(" ");
	const a = parseInt(tmp[0], 10);
	const b = parseInt(tmp[1], 10);
	const c = parseInt(tmp[2], 10);
	const d = parseInt(tmp[3], 10);
  
	console.log(Math.max(a*c,a*d,b*c,b*d,0));
  
	}

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

}