import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws NumberFormatException, IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	String input[] = br.readLine().split(" ");
	long a = Long.parseLong(input[0]);
	long b = Long.parseLong(input[1]);
	long c = Long.parseLong(input[2]);
	long d = Long.parseLong(input[3]);

	System.out.println(Math.max(Math.max(a * c, a * d), Math.max(b * c, b * d)));
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz