//package src.com.jetman.atcoder;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

/**
 * @description:
 * @author: Jetman
 * @create: 2020-08-29 14:39
 **/
public class Main {

    Scanner sc = new Scanner(System.in);

    long MOD = 1000000000 + 7;


    private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    }

    public static void main(String[] args) {
        new Main().slove();
    }
} import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.List; List java.util import java.util.Scanner; Scanner java.util public class Main {

    Scanner sc = new Scanner(System.in);

    long MOD = 1000000000 + 7;


    private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    }

    public static void main(String[] args) {
        new Main().slove();
    }
} Main Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long MOD = 1000000000 + 7; MOD 1000000000 + 7 1000000000 7 private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    } slove {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    } int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int c = sc.nextInt(); c sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc long ans = (long)a*c; ans (long)a*c (long)a c ans = Math.max(ans,(long)b*c) ans Math.max(ans,(long)b*c) Math.max Math ans (long)b*c (long)b c ans = Math.max(ans,(long)a*d) ans Math.max(ans,(long)a*d) Math.max Math ans (long)a*d (long)a d ans = Math.max(ans,(long)b*d) ans Math.max(ans,(long)b*d) Math.max Math ans (long)b*d (long)b d System.out.println(ans) System.out.println System.out System System.out ans public static void main(String[] args) {
        new Main().slove();
    } main {
        new Main().slove();
    } new Main().slove() new Main().slove new Main() String[] args args public class Main {

    Scanner sc = new Scanner(System.in);

    long MOD = 1000000000 + 7;


    private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    }

    public static void main(String[] args) {
        new Main().slove();
    }
} public class Main {

    Scanner sc = new Scanner(System.in);

    long MOD = 1000000000 + 7;


    private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    }

    public static void main(String[] args) {
        new Main().slove();
    }
} Main
//package src.com.jetman.atcoder;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

/**
 * @description:
 * @author: Jetman
 * @create: 2020-08-29 14:39
 **/
public class Main {

    Scanner sc = new Scanner(System.in);

    long MOD = 1000000000 + 7;


    private void slove() {

        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)a*c;
        ans = Math.max(ans,(long)b*c);
        ans = Math.max(ans,(long)a*d);
        ans = Math.max(ans,(long)b*d);
        System.out.println(ans);





    }

    public static void main(String[] args) {
        new Main().slove();
    }
}
