import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    }

    static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    }

    static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) BProductMax solver = new BProductMax(); solver new BProductMax() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    } BProductMax public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        } solve {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        } int a = Integer.parseInt(in.next()); a Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int b = Integer.parseInt(in.next()); b Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int c = Integer.parseInt(in.next()); c Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int d = Integer.parseInt(in.next()); d Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in long ans = 0; ans 0 if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } b <= 0 && d <= 0 b <= 0 b 0 d <= 0 d 0 {
                ans = (long) a * (long) c;
            } ans = (long) a * (long) c ans (long) a * (long) c (long) a (long) c if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a >= 0 && c >= 0 a >= 0 a 0 c >= 0 c 0 {
                ans = (long) b * (long) d;
            } ans = (long) b * (long) d ans (long) b * (long) d (long) b (long) d if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } (a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0) (a < 0 && b <= 0 && c < 0 && d <= 0) c < 0 a < 0 && b <= 0 && c < 0 && d <= 0 a < 0 a 0 b <= 0 b 0 c < 0 c 0 d <= 0 d 0 (a < 0 && b < 0 && c < 0 && d > 0) c < 0 a < 0 && b < 0 && c < 0 && d > 0 a < 0 a 0 b < 0 b 0 c < 0 c 0 d > 0 d 0 {
                ans = (long) a * (long) c;
            } ans = (long) a * (long) c ans (long) a * (long) c (long) a (long) c if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } (a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0) (a >= 0 && b > 0 && c >= 0 && d > 0) c >= 0 a >= 0 && b > 0 && c >= 0 && d > 0 a >= 0 a 0 b > 0 b 0 c >= 0 c 0 d > 0 d 0 (a > 0 && b > 0 && c < 0 && d > 0) c < 0 a > 0 && b > 0 && c < 0 && d > 0 a > 0 a 0 b > 0 b 0 c < 0 c 0 d > 0 d 0 {
                ans = (long) b * (long) d;
            } ans = (long) b * (long) d ans (long) b * (long) d (long) b (long) d if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a < 0 && b > 0 && c < 0 && d > 0 c < 0 a < 0 && b > 0 && c < 0 && d > 0 a < 0 a 0 b > 0 b 0 c < 0 c 0 d > 0 d 0 {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } ans = Math.max((long) b * (long) d, (long) a * (long) c) ans Math.max((long) b * (long) d, (long) a * (long) c) Math.max Math (long) b * (long) d (long) b (long) d (long) a * (long) c (long) a (long) c if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a < 0 && b > 0 && c > 0 && d > 0 c > 0 a < 0 && b > 0 && c > 0 && d > 0 a < 0 a 0 b > 0 b 0 c > 0 c 0 d > 0 d 0 {
                ans = (long) b * (long) d;
            } ans = (long) b * (long) d ans (long) b * (long) d (long) b (long) d if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a < 0 && b < 0 && c > 0 && d > 0 c > 0 a < 0 && b < 0 && c > 0 && d > 0 a < 0 a 0 b < 0 b 0 c > 0 c 0 d > 0 d 0 {
                ans = (long) b * (long) c;
            } ans = (long) b * (long) c ans (long) b * (long) c (long) b (long) c if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a > 0 && b > 0 && c < 0 && d < 0 c < 0 a > 0 && b > 0 && c < 0 && d < 0 a > 0 a 0 b > 0 b 0 c < 0 c 0 d < 0 d 0 {
                ans = (long) a * (long) d;
            } ans = (long) a * (long) d ans (long) a * (long) d (long) a (long) d if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a < 0 && b > 0 && c < 0 && d < 0 c < 0 a < 0 && b > 0 && c < 0 && d < 0 a < 0 a 0 b > 0 b 0 c < 0 c 0 d < 0 d 0 {
                ans = (long) a * (long) c;
            } ans = (long) a * (long) c ans (long) a * (long) c (long) a (long) c if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } b <= 0 && c >= 0 b <= 0 b 0 c >= 0 c 0 {
                ans = (long) b * (long) c;
            } ans = (long) b * (long) c ans (long) b * (long) c (long) b (long) c if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            } a >= 0 && d <= 0 a >= 0 a 0 d <= 0 d 0 {
                ans = (long) a * (long) d;
            } ans = (long) a * (long) d ans (long) a * (long) d (long) a (long) d out.println(ans) out.println out ans int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    }

    static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    }

    static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        BProductMax solver = new BProductMax();
        solver.solve(1, in, out);
        out.close();
    }

    static class BProductMax {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int a = Integer.parseInt(in.next());
            int b = Integer.parseInt(in.next());
            int c = Integer.parseInt(in.next());
            int d = Integer.parseInt(in.next());
            long ans = 0;

            if (b <= 0 && d <= 0) {
                ans = (long) a * (long) c;
            } else if (a >= 0 && c >= 0) {
                ans = (long) b * (long) d;
            } else if ((a < 0 && b <= 0 && c < 0 && d <= 0) || (a < 0 && b < 0 && c < 0 && d > 0)) {
                ans = (long) a * (long) c;
            } else if ((a >= 0 && b > 0 && c >= 0 && d > 0) || (a > 0 && b > 0 && c < 0 && d > 0)) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d > 0) {
                ans = Math.max((long) b * (long) d, (long) a * (long) c);
            } else if (a < 0 && b > 0 && c > 0 && d > 0) {
                ans = (long) b * (long) d;
            } else if (a < 0 && b < 0 && c > 0 && d > 0) {
                ans = (long) b * (long) c;
            } else if (a > 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) d;
            } else if (a < 0 && b > 0 && c < 0 && d < 0) {
                ans = (long) a * (long) c;
            } else if (b <= 0 && c >= 0) {
                ans = (long) b * (long) c;
            } else if (a >= 0 && d <= 0) {
                ans = (long) a * (long) d;
            }

            // 出力
            out.println(ans);

        }

    }
}

