import java.util.*;
import java.io.*;
class Main
{
	public static void main(String args[]) throws IOException
	{
		try{
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String arr[]=br.readLine().split(" ");
		long ans=0;
		long h=0;long p=0;
		h=Math.max(Long.parseLong(arr[0])*Long.parseLong(arr[2]),Long.parseLong(arr[0])*Long.parseLong(arr[3]));
		p=Math.max(Long.parseLong(arr[1])*Long.parseLong(arr[2]),Long.parseLong(arr[1])*Long.parseLong(arr[3]));
		ans=Math.max(h,p);
		System.out.println(ans);
		}
	catch(Exception e){}
}}
/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