import java.util.Scanner;
 
public class Main {
 
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		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);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	}
 
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) 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 bc = (long)b*c; bc (long)b*c (long)b c long bd = (long)b*d; bd (long)b*d (long)b d long ad = (long)a*d; ad (long)a*d (long)a d long ac = (long)a*c; ac (long)a*c (long)a c long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac))); ans Math.max(bc, Math.max(bd, Math.max(ad, ac))) Math.max Math bc Math.max(bd, Math.max(ad, ac)) Math.max Math bd Math.max(ad, ac) Math.max Math ad ac 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);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	}
 
} public class Main {
 
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	}
 
} Main
import java.util.Scanner;
 
public class Main {
 
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		int c = sc.nextInt();
		int d = sc.nextInt();
 
		long bc = (long)b*c;
		long bd = (long)b*d;
		long ad = (long)a*d;
		long ac = (long)a*c;
		
		long ans = Math.max(bc, Math.max(bd, Math.max(ad, ac)));
		System.out.println(ans);
	}
 
}