import java.util.*;

public class Main {
    public static void main (String args[])
    {
       
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        
        //aとbが0以下かつ
        ArrayList<Long> result = new ArrayList<>();
        
        result.add(a*c);
        result.add(a*d);
        result.add(b*c);
        result.add(b*d);

        Long max = Collections.max(result);
        System.out.println(max);
    }
}
/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