import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.util.*;
public class Main {
	
	
	public static void main(String[] args) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	}
	
	
	
	static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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.Arrays; Arrays java.util import java.util.StringTokenizer; StringTokenizer java.util import java.util.*; util.* java public class Main {
	
	
	public static void main(String[] args) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	}
	
	
	
	static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	} main {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	} FastScanner fs = new FastScanner(); fs new FastScanner() int a=fs.nextInt() a fs.nextInt() fs.nextInt fs b=fs.nextInt() b fs.nextInt() fs.nextInt fs c=fs.nextInt() c fs.nextInt() fs.nextInt fs d=fs.nextInt(); d fs.nextInt() fs.nextInt fs long product=0l; product 0l if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		} b<=0 && d<=0 b<=0 b 0 d<=0 d 0 {
			product = (long)a*c;
			System.out.println(product);
			return;
		} product = (long)a*c product (long)a*c (long)a c System.out.println(product) System.out.println System.out System System.out product return; if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		} b>=0 && d>=0 b>=0 b 0 d>=0 d 0 {
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		} product = Math.max((long)a*c, (long)b*d) product Math.max((long)a*c, (long)b*d) Math.max Math (long)a*c (long)a c (long)b*d (long)b d System.out.println(product) System.out.println System.out System System.out product return; if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		} b>=0 && c<=0 b>=0 b 0 c<=0 c 0 {
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		} product = Math.max((long)d*a,(long)c*a) product Math.max((long)d*a,(long)c*a) Math.max Math (long)d*a (long)d a (long)c*a (long)c a System.out.println(product) System.out.println System.out System System.out product return; if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		} a<=0 && d>=0 a<=0 a 0 d>=0 d 0 {
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		} product = Math.max((long)b*c,(long)a*c) product Math.max((long)b*c,(long)a*c) Math.max Math (long)b*c (long)b c (long)a*c (long)a c System.out.println(product) System.out.println System.out System System.out product return; String[] args args static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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; 
        } 
    } FastScanner BufferedReader br; br StringTokenizer st; st public FastScanner() 
        { 
            br = new BufferedReader(new
                     InputStreamReader(System.in)); 
        } FastScanner { 
            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) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	}
	
	
	
	static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	}
	
	
	
	static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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.Arrays;
import java.util.StringTokenizer;
import java.util.*;
public class Main {
	
	
	public static void main(String[] args) {
		
		FastScanner fs = new FastScanner();
		int a=fs.nextInt(), b=fs.nextInt(), c=fs.nextInt(), d=fs.nextInt();
		long product=0l;
		if(b<=0 && d<=0)
		{
			product = (long)a*c;
			System.out.println(product);
			return;
		}
		if(b>=0 && d>=0)
		{
			product = Math.max((long)a*c, (long)b*d);
			System.out.println(product);
			return;
		}
		if(b>=0 && c<=0)
		{
			product = Math.max((long)d*a,(long)c*a);
			System.out.println(product);
			return;
		}
		if(a<=0 && d>=0)
		{
			product = Math.max((long)b*c,(long)a*c);
			System.out.println(product);
			return;
		}
		
	}
	
	
	
	static class FastScanner 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() 
        { 
            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; 
        } 
    }
	
	

}
