var Main  = function(input){
    const [a, b, c, d] = input.trim().split(' ').map(x => BigInt(x));
    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"));
