function Main(input) {
	input = input.trim().split(" "); 
	var a = BigInt(input[0], 10);
	var b = BigInt(input[1], 10);
    var c = BigInt(input[2], 10);
    var d = BigInt(input[3], 10);
    
  	var ans = a * c;
  	if(a * d > ans) ans = a * d;
  	if(b * c > ans) ans = b * c;
  	if(b * d > ans) ans = b * d;

    console.log(ans.toString());
}

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