import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {
    public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

} Main public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    } main {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    } FastReader sc=new FastReader(); sc new FastReader() Long a=sc.nextLong(); a sc.nextLong() sc.nextLong sc Long b=sc.nextLong(); b sc.nextLong() sc.nextLong sc Long c=sc.nextLong(); c sc.nextLong() sc.nextLong sc Long d=sc.nextLong(); d sc.nextLong() sc.nextLong sc 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 System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4))) System.out.println System.out System System.out 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 String[] args args static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    } FastReader BufferedReader br; br StringTokenizer st; st public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        } FastReader {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        } br = new BufferedReader(new
                    InputStreamReader(System.in)) br new BufferedReader(new
                    InputStreamReader(System.in)) String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } next {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } IOException e {
                    e.printStackTrace();
                } e.printStackTrace() e.printStackTrace e {
                    st = new StringTokenizer(br.readLine());
                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } nextLine {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        } String str = ""; str "" try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                str = br.readLine();
            } str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
    public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

} public class Main {
    public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

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

public class Main {
    public static void main(String[] args) {
        FastReader sc=new FastReader();
        Long a=sc.nextLong();
        Long b=sc.nextLong();
        Long c=sc.nextLong();
        Long d=sc.nextLong();
        Long ans1=a*c;
        Long ans2=a*d;
        Long ans3=b*c;
        Long ans4=b*d;
       // System.out.println(ans1);
      //  System.out.println(ans2);
       // System.out.println(ans3);
      //  System.out.println(ans4);
        System.out.println(Math.max(Math.max(ans1,ans2),Math.max(ans3,ans4)));

    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

}
