import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Tarek
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}
 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.StringTokenizer; StringTokenizer java.util import java.io.IOException; IOException java.io import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.InputStream; InputStream java.io public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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;
        InputReader in = new InputReader(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 InputReader in = new InputReader(inputStream); in new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    } BProductMax public void solve(int testNumber, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        } solve {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        } long a = in.nextLong(); a in.nextLong() in.nextLong in long b = in.nextLong(); b in.nextLong() in.nextLong in long c = in.nextLong(); c in.nextLong() in.nextLong in long d = in.nextLong(); d in.nextLong() in.nextLong in long ans1 = a * c; ans1 a * c a c long ans2 = a * d; ans2 a * d a d long ans3 = b * c; ans3 b * c b c long ans4 = b * d; ans4 b * d b d long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4)); ans Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4)) Math.max Math Math.max(ans1, ans2) Math.max Math ans1 ans2 Math.max(ans3, ans4) Math.max Math ans3 ans4 out.println(ans) out.println out ans int testNumber testNumber InputReader in in PrintWriter out out static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Tarek
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(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, InputReader in, PrintWriter out) {
            long a = in.nextLong();
            long b = in.nextLong();
            long c = in.nextLong();
            long d = in.nextLong();
            long ans1 = a * c;
            long ans2 = a * d;
            long ans3 = b * c;
            long ans4 = b * d;
            long ans = Math.max(Math.max(ans1, ans2), Math.max(ans3, ans4));
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}

