import java.io.BufferedReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {
    
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new java.io.InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);
        StringTokenizer st = new StringTokenizer(br.readLine());

        long a = Long.parseLong(st.nextToken());
        long b = Long.parseLong(st.nextToken());
        long c = Long.parseLong(st.nextToken());
        long d = Long.parseLong(st.nextToken());
        
        long ans1 = a * c;
        long ans2 = a * d;
        long ans3 = b * c;
        long ans4 = b * d;

        long[] ans_array = {ans1, ans2, ans3, ans4};

        Arrays.sort(ans_array);

        pw.println(ans_array[3]);
        br.close();
        pw.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