import java.util.*; 
import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    }
    static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    }

} import java.util.*; util.* java import java.io.*; io.* java public class Main {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    }
    static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    }

} Main public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    } main {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) PrintWriter pw = new PrintWriter(System.out); pw new PrintWriter(System.out) 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 ans = (long)-4e18; ans (long)-4e18 4e18 ans=Math.max(ans,1l*a*c) ans Math.max(ans,1l*a*c) Math.max Math ans 1l*a*c 1l*a*c 1l a c ans=Math.max(ans,1l*a*d) ans Math.max(ans,1l*a*d) Math.max Math ans 1l*a*d 1l*a*d 1l a d ans=Math.max(ans,1l*b*c) ans Math.max(ans,1l*b*c) Math.max Math ans 1l*b*c 1l*b*c 1l b c ans=Math.max(ans,1l*b*d) ans Math.max(ans,1l*b*d) Math.max Math ans 1l*b*d 1l*b*d 1l b d pw.println(ans) pw.println pw ans pw.flush() pw.flush pw String[] args args static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    } Scanner BufferedReader br; br StringTokenizer st; st public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        } Scanner {
            br = new BufferedReader(new InputStreamReader(s));
        } br = new BufferedReader(new InputStreamReader(s)) br new BufferedReader(new InputStreamReader(s)) InputStream s s public Scanner(FileReader f) {
            br = new BufferedReader(f);
        } Scanner {
            br = new BufferedReader(f);
        } br = new BufferedReader(f) br new BufferedReader(f) FileReader f f public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        } next {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        } while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine()); st == null || !st.hasMoreTokens() st == null st null !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st public int nextInt() throws IOException {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public long nextLong() throws IOException {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        } nextIntArr {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        } int[] arr = new int[n]; arr new int[n] n for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
                arr[i] = Integer.parseInt(next());
            } {
                arr[i] = Integer.parseInt(next());
            } arr[i] = Integer.parseInt(next()) arr[i] arr i Integer.parseInt(next()) Integer.parseInt Integer next() next return arr; arr int n n public class Main {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    }
    static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    }

} public class Main {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    }
    static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    }

} Main
import java.util.*; 
import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int a= sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long ans = (long)-4e18;
        ans=Math.max(ans,1l*a*c);
        ans=Math.max(ans,1l*a*d);
        ans=Math.max(ans,1l*b*c);
        ans=Math.max(ans,1l*b*d);
        pw.println(ans);
        pw.flush();
    }
    static class Scanner {
        BufferedReader br;
        StringTokenizer st;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader f) {
            br = new BufferedReader(f);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

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

        public double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        public int[] nextIntArr(int n) throws IOException {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = Integer.parseInt(next());
            }
            return arr;
        }

    }

}