var Main  = function(input){
    var nums=input.split(" ").map((n)=>parseInt(n,10));
    var a = nums[0];
    var b = nums[1];
    var c = nums[2];
    var d = nums[3];

    var array=[];

    array.push(a*c,a*d,b*c,b*d);
    array.sort(function (x,y){return y-x;});

    console.log(array[0]+0);
};


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