// ************************* J A I  S H R E E  R A M  *************************


/*

      :: All is One ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

      Author: Udit "luctivud" Gupta
      linkedin : (https://www.linkedin.com/in/udit-gupta-1b7863135/)

      My original ids go by the username @luctivud
      However, if summoned, my alts can surround your surroundings in a flash.

      Do you know Hairu Ihei ?

      :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: One is All ::


*/


#include <bits/stdc++.h>

#pragma GCC optimize "trapv"
#pragma GCC optimize ("Ofast")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize ("-ffloat-store")


using namespace std;



typedef long long int lld;
typedef unsigned long long int llu;

#define         TESTCASES()    cin >> (T3X0); T353 = T3X0; while(T3X0--)
#define          input(V3C)    for(auto &V3C_I7 : (V3C)) cin >> (V3C_I7)
#define   mems(A77AY, V4LU)    memset((A77AY), (V4LU), sizeof((A77AY)))
#define    CH3K(I7, E4, S7)    (((S7)>0) ? (I7)<(E4) : (I7)>(E4))
#define   for4(I7,S4,E4,S7)    for(auto I7=(S4); CH3K(I7,E4,S7); (I7)+=(S7))
#define        forn(I7, E4)    for(lld I7=0ll; I7 < E4; (I7)+=1ll)
#define       forn1(I7, E4)    for(lld I7=1ll; I7 < E4+1; (I7)+=1ll)
#define        EACH(I7, A7)    for (auto& I7: A7)
#define              len(v)    ((int)((v).size()))
#define              all(x)    (x).begin(), (x).end()
#define             rall(x)    (x).rbegin(), (x).rend()
#define                  pb    push_back
#define         debhairu(x)    cout << #x << " = "; println(x);
#define         debspace(x)    cout << #x << " = "; print(x); cout << " ";
#define                  f1    first
#define                  s2    second



#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); huehue(_it, args); cout << "\n";}

void huehue(istream_iterator<string> it) {}
template<typename T, typename... Args>
void huehue(istream_iterator<string> it, T a, Args... args) {
	cout << *it << " = " << a << ", ";
	huehue(++it, args...);
}


template <class T> T inf() {
	return numeric_limits<T>::max();
}


void read() { return; }
void print() { return; }
void println() { cout << "\n"; return; }
template<class T> T read(T& x)   { cin >> x; return x; }
template<class T> void print(T a)   { cout << a; }
template<class T> void println(T a) { cout << a << "\n"; }

template<class T> void read(vector<T> &arr)   { EACH(i, arr) cin >> (i); }
template<class T> void print(vector<T> arr)   { EACH(i, arr) {cout << i << " ";} }
template<class T> void println(vector<T> arr) { EACH(i, arr) {cout << i << " ";} cout << "\n"; }

template<class T> void read(vector<vector<T>> &arr)   { EACH(i, arr) read(i); }
template<class T> void print(vector<vector<T>> arr)   { EACH(i, arr) println(i); }
template<class T> void println(vector<vector<T>> arr) { EACH(i, arr) println(i); }

template<typename T, typename... Args> void read(vector<T> &arr, Args &... args)   { read(arr); read(args...);}
template<typename T, typename... Args> void read(vector<vector<T>> &arr, Args &... args)   { read(arr); read(args...);}
template<typename T, typename... Args> void read(T &a, Args &... args) { cin >> (a); read(args...); }
template<typename T, typename... Args> void print(vector<T> &arr, Args &... args)   { print(arr); print(args...);}
template<typename T, typename... Args> void print(T a, Args... args) { cout << a << " "; print(args...); };
template<typename T, typename... Args> void println(vector<T> &arr, Args &... args)   { print(arr); println(args...);}
template<typename T, typename... Args> void println(T a, Args... args) { cout << a << " "; println(args...); };


const lld d4i[4] = { -1, 0, 1, 0}, d4j[4] = {0, 1, 0, -1};
const lld d8i[8] = { -1, -1, 0, 1, 1, 1, 0, -1}, d8j[8] = {0, 1, 1, 1, 0, -1, -1, -1};

const auto start_time = std::chrono::high_resolution_clock::now();
signed luctivud() {

#ifdef LUCTIVUD
	//your code for local things
	auto end_time = std::chrono::high_resolution_clock::now();
	std::chrono::duration<double> diff = end_time - start_time;
	cerr << "Finished in : " << diff.count() << "\n";
#endif

	return 0;
}


///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////





void solveEachTest(lld _TestCase) {
	// cout << "Case#" << _TestCase << ": ";
	lld a, b, c, d; read(a, b, c, d);
	println(max({a * d, b * c, a * c, b * d}));

	// cout << "\n";
	return;
}


signed main() {
	ios_base::sync_with_stdio(false); cin.tie(0);
	cout.precision(10); cout << fixed;

	lld T3X0 = 0, T353 = 1;

	// TESTCASES()
	solveEachTest(T353 - T3X0);

	return luctivud();
}

// Random Thought :  null
/*
        Grab my throat and lift me in the air!
*/


Measured memory_bytes: 3628