import java.io.*;
import java.math.*;
import java.util.*;
public class Main {
	static long mod = (long)(1e9+7);
	public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	}
	public static double max(double a, double b) {return Math.max(a, b);}
	public static double min(double a, double b) {return Math.min(a, b);}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static int max(int a, int b) {return Math.max(a,b);}
	public static long abs(long x) {return Math.abs(x);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	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());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
} import java.io.*; io.* java import java.math.*; math.* java import java.util.*; util.* java public class Main {
	static long mod = (long)(1e9+7);
	public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	}
	public static double max(double a, double b) {return Math.max(a, b);}
	public static double min(double a, double b) {return Math.min(a, b);}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static int max(int a, int b) {return Math.max(a,b);}
	public static long abs(long x) {return Math.abs(x);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	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());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
} Main static long mod = (long)(1e9+7); mod (long)(1e9+7) 1e9 7 public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	} main { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	} FastScanner I = new FastScanner(); I new FastScanner() OutPut O = new OutPut(); O new OutPut() long a  = I.nextLong(); a I.nextLong() I.nextLong I long b  = I.nextLong(); b I.nextLong() I.nextLong I long c  = I.nextLong(); c I.nextLong() I.nextLong I long d  = I.nextLong(); d I.nextLong() I.nextLong I long ans = Long.MIN_VALUE; ans Long.MIN_VALUE Long Long.MIN_VALUE ans=max(ans,a*c) ans max(ans,a*c) max ans a*c a c ans=max(ans,b*c) ans max(ans,b*c) max ans b*c b c ans=max(ans,a*d) ans max(ans,a*d) max ans a*d a d ans=max(ans,b*d) ans max(ans,b*d) max ans b*d b d O.pln(ans) O.pln O ans String[] args args public static double max(double a, double b) {return Math.max(a, b);} max {return Math.max(a, b);} return Math.max(a, b); Math.max(a, b) Math.max Math a b double a a double b b public static double min(double a, double b) {return Math.min(a, b);} min {return Math.min(a, b);} return Math.min(a, b); Math.min(a, b) Math.min Math a b double a a double b b public static long min(long a, long b) {return Math.min(a,b);} min {return Math.min(a,b);} return Math.min(a,b); Math.min(a,b) Math.min Math a b long a a long b b public static long max(long a, long b) {return Math.max(a,b);} max {return Math.max(a,b);} return Math.max(a,b); Math.max(a,b) Math.max Math a b long a a long b b public static int min(int a, int b) {return Math.min(a,b);} min {return Math.min(a,b);} return Math.min(a,b); Math.min(a,b) Math.min Math a b int a a int b b public static int max(int a, int b) {return Math.max(a,b);} max {return Math.max(a,b);} return Math.max(a,b); Math.max(a,b) Math.max Math a b int a a int b b public static long abs(long x) {return Math.abs(x);} abs {return Math.abs(x);} return Math.abs(x); Math.abs(x) Math.abs Math x long x x public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;} ceil {long ans = num/den; if (num%den!=0) 
	ans++; return ans;} long ans = num/den; ans num/den num den if (num%den!=0) 
	ans++; num%den!=0 num%den num den 0 ans++ ans return ans; ans long num num long den den public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	} GCD {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	} if (a==0||b==0) return max(a,b); a==0||b==0 a==0 a 0 b==0 b 0 return max(a,b); max(a,b) max a b return GCD(min(a,b),max(a,b)%min(a,b)); GCD(min(a,b),max(a,b)%min(a,b)) GCD min(a,b) min a b max(a,b)%min(a,b) max(a,b) max a b min(a,b) min a b long a a long b b public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	} FastExp {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	} long ans=1; ans 1 while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		} exp>0 exp 0 {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		} if (exp%2==1) ans*=base; exp%2==1 exp%2 exp 2 1 ans*=base ans base exp/=2 exp 2 base*=base base base base%=mod base mod ans%=mod ans mod return ans; ans long base base long exp exp long mod mod public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);} ModInv {return FastExp(num,mod-2,mod);} return FastExp(num,mod-2,mod); FastExp(num,mod-2,mod) FastExp num mod-2 mod 2 mod long num num long mod mod public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	} pop { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	} int cnt = 0; cnt 0 while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		} x>0 x 0 {
			if (x%2==1) cnt++;
			x/=2;
		} if (x%2==1) cnt++; x%2==1 x%2 x 2 1 cnt++ cnt x/=2 x 2 return cnt; cnt long x x 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());};
		double nextDouble() {return Double.parseDouble(next());}
	} 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 double nextDouble() {return Double.parseDouble(next());} nextDouble {return Double.parseDouble(next());} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	} OutPut PrintWriter w = new PrintWriter(System.out); w new PrintWriter(System.out) void pln(double x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w double x x void pln(boolean x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w boolean x x void pln(int x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w int x x void pln(long x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w long x x void pln(String x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w String x x void pln(char x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w char x x void pln(StringBuilder x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w StringBuilder x x void pln(BigInteger x) {w.println(x);w.flush();} pln {w.println(x);w.flush();} w.println(x) w.println w x w.flush() w.flush w BigInteger x x void p(int x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w int x x void p(long x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w long x x void p(String x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w String x x void p(char x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w char x x void p(StringBuilder x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w StringBuilder x x void p(BigInteger x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w BigInteger x x void p(double x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w double x x void p(boolean x) {w.print(x);w.flush();} p {w.print(x);w.flush();} w.print(x) w.print w x w.flush() w.flush w boolean x x public class Main {
	static long mod = (long)(1e9+7);
	public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	}
	public static double max(double a, double b) {return Math.max(a, b);}
	public static double min(double a, double b) {return Math.min(a, b);}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static int max(int a, int b) {return Math.max(a,b);}
	public static long abs(long x) {return Math.abs(x);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	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());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
} public class Main {
	static long mod = (long)(1e9+7);
	public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	}
	public static double max(double a, double b) {return Math.max(a, b);}
	public static double min(double a, double b) {return Math.min(a, b);}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static int max(int a, int b) {return Math.max(a,b);}
	public static long abs(long x) {return Math.abs(x);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	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());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
} Main
import java.io.*;
import java.math.*;
import java.util.*;
public class Main {
	static long mod = (long)(1e9+7);
	public static void main(String[] args) { //Ball out 
		/*
		 * */
		FastScanner I = new FastScanner(); //Input
		OutPut O = new OutPut(); //Output
		long a  = I.nextLong();
		long b  = I.nextLong();
		long c  = I.nextLong();
		long d  = I.nextLong();
		long ans = Long.MIN_VALUE;
		ans=max(ans,a*c);
		ans=max(ans,b*c);
		ans=max(ans,a*d);
		ans=max(ans,b*d);
		O.pln(ans);
	}
	public static double max(double a, double b) {return Math.max(a, b);}
	public static double min(double a, double b) {return Math.min(a, b);}
	public static long min(long a, long b) {return Math.min(a,b);}
	public static long max(long a, long b) {return Math.max(a,b);}
	public static int min(int a, int b) {return Math.min(a,b);}
	public static int max(int a, int b) {return Math.max(a,b);}
	public static long abs(long x) {return Math.abs(x);}
	public static long ceil(long num, long den) {long ans = num/den; if (num%den!=0) 
	ans++; return ans;}
	public static long GCD(long a, long b) {
		if (a==0||b==0) return max(a,b);
		return GCD(min(a,b),max(a,b)%min(a,b));
	}
	public static long FastExp(long base, long exp, long mod) {
		long ans=1;
		while (exp>0) {
			if (exp%2==1) ans*=base;
			exp/=2;
			base*=base;
			base%=mod;
			ans%=mod;
		}
		return ans;
	}
	public static long ModInv(long num,long mod) {return FastExp(num,mod-2,mod);}
	public static int pop(long x) { //Returns number of bits within a number
		int cnt = 0;
		while (x>0) {
			if (x%2==1) cnt++;
			x/=2;
		}
		return cnt;
	}
	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());};
		double nextDouble() {return Double.parseDouble(next());}
	}
	static class OutPut{
		PrintWriter w = new PrintWriter(System.out);
		void pln(double x) {w.println(x);w.flush();}
		void pln(boolean x) {w.println(x);w.flush();}
		void pln(int x) {w.println(x);w.flush();}
		void pln(long x) {w.println(x);w.flush();}
		void pln(String x) {w.println(x);w.flush();}
		void pln(char x) {w.println(x);w.flush();}
		void pln(StringBuilder x) {w.println(x);w.flush();}
		void pln(BigInteger x) {w.println(x);w.flush();}
		void p(int x) {w.print(x);w.flush();}
		void p(long x) {w.print(x);w.flush();}
		void p(String x) {w.print(x);w.flush();}
		void p(char x) {w.print(x);w.flush();}
		void p(StringBuilder x) {w.print(x);w.flush();}
		void p(BigInteger x) {w.print(x);w.flush();}
		void p(double x) {w.print(x);w.flush();}
		void p(boolean x) {w.print(x);w.flush();}
	}
}
