import java.util.*;
public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc =new Scanner(System.in);
        long[] line =new long[4];
        for (int i = 0; i < 4; i++) {
            line[i] = sc.nextLong();  
        }
        long max = Long.MIN_VALUE;
        
        for (int i = 0; i < 2; i++) {
            for (int j = 2; j < 4; j++) {
                max = Math.max(max, line[i]*line[j]);
            }
        }

        System.out.println(max);
		sc.close();
    }
}

/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