
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();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  }
} import java.util.*; util.* java 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();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  }
} 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();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    long a = sc.nextLong();
    long b = sc.nextLong();
    long c = sc.nextLong();
    long d = sc.nextLong();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long a = sc.nextLong(); a sc.nextLong() sc.nextLong sc long b = sc.nextLong(); b sc.nextLong() sc.nextLong sc long c = sc.nextLong(); c sc.nextLong() sc.nextLong sc long d = sc.nextLong(); d sc.nextLong() sc.nextLong sc long ans = (a * c); ans (a * c) a c ans = Math.max(ans, a * d) ans Math.max(ans, a * d) Math.max Math ans a * d a d ans = Math.max(ans, b * c) ans Math.max(ans, b * c) Math.max Math ans b * c b c ans = Math.max(ans, b * d) ans Math.max(ans, b * d) Math.max Math ans b * d b d System.out.println(ans) System.out.println System.out System System.out ans String[] args args 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();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  }
} 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();
    long ans = (a * c);
    ans = Math.max(ans, a * d);
    ans = Math.max(ans, b * c);
    ans = Math.max(ans, b * d);
    System.out.println(ans);
  }
} Main

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