// Born Sinner
// old but im not that old
// fuck all you hoes get a grip
import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
    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 (Exception e){
                e.printStackTrace();
            }
            return str;
        }
    }
    static int modPower(int x, int y, int mod){
        int res = 1;
        x %= mod;
        if(x==0) return 0;
        while(y>0){
            if(y%2==1){
                res = (res*x)%mod;
            }
            y = y>>1;
            x = (x*x)%mod;
        }
        return res;
    }
    static class pair<T1, T2>{
        T1 first;
        T2 second;
        pair(T1 first, T2 second){
            this.first = first;
            this.second = second;
        }
    }
    
    public static void main (String[] args) throws java.lang.Exception
    {
        FastReader in = new FastReader();
        long[] a = new long[4];
        for(int i = 0; i < 4; i++) a[i]=in.nextLong();
        System.out.println(Math.max(a[0]*a[2], Math.max(a[1]*a[3], Math.max(a[0]*a[3], a[1]*a[2]))));
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz