function Main(input) {
    var inArray = input.split(' ')

    var a = parseInt(inArray[0]);
    var b = parseInt(inArray[1]);
    var c = parseInt(inArray[2]);
    var d = parseInt(inArray[3]);
    
    var r = Math.max.apply(null, [a*c, a*d, b*c, b*d]);

    console.log(r)
    

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