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

public class Main {
	
	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	}
	
	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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
	
	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	}
	
	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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
} Main public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	} main {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	} FastScanner fs = new FastScanner(); fs new FastScanner() long 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 ans = Long.MAX_VALUE; ans Long.MAX_VALUE Long Long.MAX_VALUE 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 long temp1 = Math.max(ans1, ans2); temp1 Math.max(ans1, ans2) Math.max Math ans1 ans2 long temp2 = Math.max(ans3, ans4); temp2 Math.max(ans3, ans4) Math.max Math ans3 ans4 ans = Math.max(temp1, temp2) ans Math.max(temp1, temp2) Math.max Math temp1 temp2 System.out.println(ans) System.out.println System.out System System.out ans String[] args args 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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(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 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 long nextLong() {
			return Long.parseLong(next());
		} nextLong {
			return Long.parseLong(next());
		} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public class Main {
	
	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	}
	
	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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
} public class Main {
	
	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	}
	
	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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
} Main
import java.util.*;
import java.io.*;

public class Main {
	
	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner();
		long a = fs.nextInt() , b = fs.nextInt(), c = fs.nextInt(), d = fs.nextInt();
		long ans = Long.MAX_VALUE;
		long ans1 = a*c;
		long ans2 = a*d;
		long ans3 = b*c;
		long ans4 = b*d;
		long temp1 = Math.max(ans1, ans2);
		long temp2 = Math.max(ans3, ans4);
		ans = Math.max(temp1, temp2);
		System.out.println(ans);
	}
	
	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());
		}
		int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}
		long nextLong() {
			return Long.parseLong(next());
		}
	}
}
