import java.util.Scanner;

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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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.Scanner; Scanner 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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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 sc.close() sc.close sc long ans = -1000000000000000000L; ans -1000000000000000000L 1000000000000000000L ans = Math.max(ans, a*c) ans Math.max(ans, a*c) Math.max Math 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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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.Scanner;

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();
//		String[] array = new String[n];
//		for(int i=0;i<n;i++) {
//				array[i] = sc.next();
//		}
		sc.close();

		long ans = -1000000000000000000L;

		ans = Math.max(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);
	}
}
