import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	} 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 temp = 0; temp 0 temp = a * c temp a * c a c if(temp < a * d) temp = a * d; temp < a * d temp a * d a d temp = a * d temp a * d a d if(temp < b * c) temp = b * c; temp < b * c temp b * c b c temp = b * c temp b * c b c if(temp < b * d) temp = b * d; temp < b * d temp b * d b d temp = b * d temp b * d b d System.out.println(temp) System.out.println System.out System System.out temp String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();
		
		long temp = 0;
		temp = a * c;
		if(temp < a * d) temp = a * d;
		if(temp < b * c) temp = b * c;
		if(temp < b * d) temp = b * d;
		
		System.out.println(temp);
	}

}
