const main = (arg) => {
  	let [a,b,c,d] = arg.split(" ").map(Number)

    let [m1,m2,m3,m4] = [a*c,a*d,b*c,b*d]
    console.log(Math.max(m1,m2,m3,m4))
}
main(require("fs").readFileSync("/dev/stdin", "utf8"));