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

public class Main {

	public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	}
	
	static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	}
	
	static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	}
	
	static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	}
	
	static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	}
	
	static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	}
	
	static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	}
}
 import java.io.*; io.* java import java.util.*; util.* java public class Main {

	public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	}
	
	static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	}
	
	static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	}
	
	static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	}
	
	static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	}
	
	static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	}
	
	static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	}
} Main public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	} main {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	} FastScanner in = new FastScanner(); in new FastScanner() PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) long a = in.nextInt() a in.nextInt() in.nextInt in b = in.nextInt() b in.nextInt() in.nextInt in c = in.nextInt() c in.nextInt() in.nextInt in d = in.nextInt(); d in.nextInt() in.nextInt in out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d))) out.println out Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)) Math.max Math Math.max(a*c, a*d) Math.max Math a*c a c a*d a d Math.max(b*c, b*d) Math.max Math b*c b c b*d b d out.flush() out.flush out String[] args args static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	} arrayEquals {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	} int n = a.length; n a.length a a.length boolean verdict = true; verdict true for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		} {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		} if(a[i]!=b[i]) {
				verdict = false;break;
			} a[i]!=b[i] a[i] a i b[i] b i {
				verdict = false;break;
			} verdict = false verdict false break; return verdict; verdict char a[] a char b[] b static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	} lcm {
		return (a*b)/gcd(a,b);
	} return (a*b)/gcd(a,b); (a*b)/gcd(a,b) (a*b) a b gcd(a,b) gcd a b long a a long b b static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	} gcd {
		if(b==0) return a;
		else return gcd(b,a%b);
	} if(b==0) return a;
		else return gcd(b,a%b); b==0 b 0 return a; a return gcd(b,a%b); gcd(b,a%b) gcd b a%b a b long a a long b b static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	} hashInt {
		return x*(1_000_000_000L)+y;
	} return x*(1_000_000_000L)+y; x*(1_000_000_000L)+y x*(1_000_000_000L) x (1_000_000_000L) y int x x int y y static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	} FastScanner BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) StringTokenizer st = new StringTokenizer(""); st new StringTokenizer("") String next() {
			while(!st.hasMoreTokens())
				try {
					st = new StringTokenizer(br.readLine());
				}catch(IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} next {
			while(!st.hasMoreTokens())
				try {
					st = new StringTokenizer(br.readLine());
				}catch(IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} while(!st.hasMoreTokens())
				try {
					st = new StringTokenizer(br.readLine());
				}catch(IOException e) {
					e.printStackTrace();
				} !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st 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 int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		} readArray {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		} int a[] = new int[n]; a new int[n] n for(int i=0;i<n;i++) a[i] = nextInt(); int i=0; int i=0; i 0 i<n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		} readArray {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		} Integer a[] = new Integer[(int)n]; a new Integer[(int)n] (int)n for(int i=0;i<n;i++) a[i] = nextInt(); int i=0; int i=0; i 0 i<n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a long n n long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		} readArray {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		} long a[] = new long[n]; a new long[n] n for(int i=0;i<n;i++) a[i] = nextLong(); int i=0; int i=0; i 0 i<n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n long x x static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	} Pair int x x y; y Pair(int a, int b){ x = a; y = b; } Pair { x = a; y = b; } x = a x a y = b y b int a a int b b int getKey() { return x; } getKey { return x; } return x; x int getVal() { return y; } getVal { return y; } return y; y @Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		} compareTo {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		} if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0; o.getVal() - this.getVal()>0 o.getVal() - this.getVal() o.getVal() o.getVal o this.getVal() this.getVal this 0 return -1; -1 1 if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0; o.getVal() - this.getVal()<0 o.getVal() - this.getVal() o.getVal() o.getVal o this.getVal() this.getVal this 0 return 1; 1 return 0; 0 Pair o o Comparable public class Main {

	public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	}
	
	static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	}
	
	static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	}
	
	static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	}
	
	static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	}
	
	static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	}
	
	static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	}
} public class Main {

	public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	}
	
	static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	}
	
	static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	}
	
	static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	}
	
	static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	}
	
	static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	}
	
	static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	}
} Main
import java.io.*;
import java.util.*;

public class Main {

	public static void main(String[] args) {
        FastScanner in = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);
        long a = in.nextInt() , b = in.nextInt() , c = in.nextInt() , d = in.nextInt();
        out.println(Math.max(Math.max(a*c, a*d), Math.max(b*c, b*d)));
        out.flush();
	}
	
	static class FastScanner {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");
		
		String next() {
			while(!st.hasMoreTokens())
				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());
		}
		
		int[] readArray(int n) {
			int a[] = new int[n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		Integer[] readArray(long n) {
		    Integer a[] = new Integer[(int)n];
			for(int i=0;i<n;i++) a[i] = nextInt();
			return a;
		}
		
		long[] readArray(int n,long x) {
			long a[] = new long[n];
			for(int i=0;i<n;i++) a[i] = nextLong();
			return a;
		}
		
	}
	
	static class Pair implements Comparable<Pair> {
		int x, y;
		Pair(int a, int b){ x = a; y = b; }
		int getKey() { return x; }
		int getVal() { return y; }
		@Override
		public int compareTo(Pair o) {
			if(o.getVal() - this.getVal()>0)
				return -1;
			else if(o.getVal() - this.getVal()<0)
				return 1;
			else 
				return 0;
		}
		
	}
	
	static boolean arrayEquals(char a[], char b[]) {
		int n = a.length;
		boolean verdict = true;
		for(int i=0;i<n;i++) {
			if(a[i]!=b[i]) {
				verdict = false;break;
			}
		}
		return verdict;
	}
	
	static long lcm(long a, long b) {
		return (a*b)/gcd(a,b);
	}
	
	static long gcd(long a, long b) {
		if(b==0) return a;
		else return gcd(b,a%b);
	}
	
	static long hashInt(int x,int y) {
		return x*(1_000_000_000L)+y;
	}
}

