import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;

class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;
    static final int ALF = 26;

    Main() {
        Scanner sc = new Scanner(System.in);
        long ans = 0;
        long A = sc.nextInt();
        long B = sc.nextInt();
        long C = sc.nextInt();
        long D = sc.nextInt();
        ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D)));//Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,)))))))))
        System.out.println(ans);
    }

    public static void main(String[] args) {
        new Main();
    }
} import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Collections; Collections java.util import java.util.Comparator; Comparator java.util import java.util.HashMap; HashMap java.util import java.util.HashSet; HashSet java.util import java.util.Iterator; Iterator java.util import java.util.List; List java.util import java.util.Map.Entry; Entry java.util.Map import java.util.PriorityQueue; PriorityQueue java.util import java.util.Scanner; Scanner java.util class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;
    static final int ALF = 26;

    Main() {
        Scanner sc = new Scanner(System.in);
        long ans = 0;
        long A = sc.nextInt();
        long B = sc.nextInt();
        long C = sc.nextInt();
        long D = sc.nextInt();
        ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D)));//Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,)))))))))
        System.out.println(ans);
    }

    public static void main(String[] args) {
        new Main();
    }
} Main static final int MOD = 1000000007; MOD 1000000007 static final int INF = 1 << 30; INF 1 << 30 1 30 static final int ALF = 26; ALF 26 Main() {
        Scanner sc = new Scanner(System.in);
        long ans = 0;
        long A = sc.nextInt();
        long B = sc.nextInt();
        long C = sc.nextInt();
        long D = sc.nextInt();
        ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D)));//Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,)))))))))
        System.out.println(ans);
    } Main {
        Scanner sc = new Scanner(System.in);
        long ans = 0;
        long A = sc.nextInt();
        long B = sc.nextInt();
        long C = sc.nextInt();
        long D = sc.nextInt();
        ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D)));//Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,)))))))))
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long ans = 0; ans 0 long A = sc.nextInt(); A sc.nextInt() sc.nextInt sc long B = sc.nextInt(); B sc.nextInt() sc.nextInt sc long C = sc.nextInt(); C sc.nextInt() sc.nextInt sc long D = sc.nextInt(); D sc.nextInt() sc.nextInt sc ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D))) ans Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D))) Math.max Math A*C A C Math.max(A*D,Math.max(B*C,B*D)) Math.max Math A*D A D Math.max(B*C,B*D) Math.max Math B*C B C B*D B D System.out.println(ans) System.out.println System.out System System.out ans public static void main(String[] args) {
        new Main();
    } main {
        new Main();
    } new Main() String[] args args
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import java.util.PriorityQueue;
import java.util.Scanner;

class Main {
    static final int MOD = 1000000007;
    static final int INF = 1 << 30;
    static final int ALF = 26;

    Main() {
        Scanner sc = new Scanner(System.in);
        long ans = 0;
        long A = sc.nextInt();
        long B = sc.nextInt();
        long C = sc.nextInt();
        long D = sc.nextInt();
        ans = Math.max(A*C,Math.max(A*D,Math.max(B*C,B*D)));//Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,Math.max(,)))))))))
        System.out.println(ans);
    }

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