import java.util.*;

public class Main
{
    public static void main(String[] args) {
        //long start = System.currentTimeMillis();
        Scanner sc = new Scanner(System.in);
        long[] a = new long[2];
        long[] b = new long[2];
        a[0] = sc.nextLong();
        a[1] = sc.nextLong();
        b[0] = sc.nextLong();
        b[1] = sc.nextLong();

        long max = Long.MIN_VALUE;
        for (int i = 0;i<2;++i)
        {
            for (int j = 0;j<2;++j)
            {
                long tmp = a[i]*b[j];
                max = Math.max(tmp,max);
            }
        }
        System.out.println(max);
        sc.close();
//        long end = System.currentTimeMillis();
//        System.err.println((end-start)+"ms");
    }
}
/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