using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;
using static MyExtention;
class MainClass : Scanner
{
    static void Main()
    {
        var (a,b,c,d) = ReadTuple<long,long,long,long>();
        long ans = Max(b * d, a * d, a * c, b * c);
        WriteLine(ans);
    }
}

class MyExtention
{
    public static long GCD(long a, long b)
        => a == 0 ? b : GCD(b % a, a);
    public static long LCM(long a, long b)
        => a / GCD(a, b) * b;

    public static long ModPow(long a, long n, long Mod) //未テスト　オーバーフローの可能性あり
    {
        long ans = 1;
        while (n > 0)
        {
            if (n % 2 == 1)
                ans = ans * a % Mod;
            a = a * a % Mod;
            n /= 2;
        }
        return ans;
    }
    public static T Max<T>(params T[] nums) where T : IComparable
    {
        T max = nums[0];
        for (int i = 1; i < nums.Length; i++)
        {
            if (max.CompareTo(nums[i]) < 0) max = nums[i];
        }
        return max;
    }
    public static T Min<T>(params T[] nums) where T : IComparable
    {
        T min = nums[0];
        for (int i = 1; i < nums.Length; i++)
        {
            if (min.CompareTo(nums[i]) > 0) min = nums[i];
        }
        return min;
    }


}

class Scanner
{
    public static string RString() => Console.ReadLine();
    public static int RInt() => ReadTuple<int>();
    public static long RLong() => ReadTuple<long>();
    public static double RDouble() => ReadTuple<double>();

    public static string[] RStrings() => Console.ReadLine().Split();
    public static int[] RInts() => Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
    public static long[] RLongs() => Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
    public static double[] RDoubles() => Array.ConvertAll(Console.ReadLine().Split(), double.Parse);
    public static int[] RInts(Func<string, int> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static long[] RLongs(Func<string, long> func) => Console.ReadLine().Split().Select(func).ToArray();
    public static double[] RDoubles(Func<string, double> func) => Console.ReadLine().Split().Select(func).ToArray();
    //public static string[] RStrings(Func<string, string> func) => Console.ReadLine().Split().Select(func).ToArray();

    public static T1 ReadTuple<T1>()
    {
        var r = RString();
        var r1 = (T1)Convert.ChangeType(r, typeof(T1));
        return r1;
    }
    public static (T1, T2) ReadTuple<T1, T2>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        return (r1, r2);
    }
    public static (T1, T2, T3) ReadTuple<T1, T2, T3>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        return (r1, r2, r3);
    }
    public static (T1, T2, T3, T4) ReadTuple<T1, T2, T3, T4>()
    {
        var r = RStrings();
        var r1 = (T1)Convert.ChangeType(r[0], typeof(T1));
        var r2 = (T2)Convert.ChangeType(r[1], typeof(T2));
        var r3 = (T3)Convert.ChangeType(r[2], typeof(T3));
        var r4 = (T4)Convert.ChangeType(r[3], typeof(T4));
        return (r1, r2, r3, r4);
    }
}


Measured memory_bytes: 27576