function Main(input) {
    var num = input.split(' ');

    var a = parseInt(num[0], 10);
    var b = parseInt(num[1], 10);
    var c = parseInt(num[2], 10);
    var d = parseInt(num[3], 10);

    var r = Math.max(a*c, a*d, b*c, b*d);
    console.log(r)
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));