/*Never Give up -- Life is to short to make mistakes and learn from them -- Learn from other's mistakes*/

/*Waiting to become purple */

#include <iostream>
#include <cstdio>
#include <numeric>
#include <ctime>
#include <cstring>
#include <cstdlib>
#include <iomanip>
#include <cmath>
#include <climits>
#include <vector>
#include <bitset>
#include <set>
#include <queue>
#include <stack>
#include <map>
#include <deque>
#include <string>
#include <list>
#include <iterator>
#include <algorithm>
#include <unordered_map>
#define int                long long
#define pb                 push_back
#define pi                 pair<int,int>
#define vi                 vector<int>
#define all(v)             v.begin(),v.end()
#define MOD                1000000007
#define F                  first
#define S                  second
#define FOR(i,r)           for(int i=0;i<r;i++)
#define REP(i,l,r)         for(int i=l;i<r;i++)
#define RER(i,l,r)         for(int i=l;i>=r;i--)
#define print(v)           for(auto i : v)cout << i << ' ';
#define FASTIO             ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define mem(arr,k)         memset(arr,k,sizeof(arr));
#define pii                acos(-1.0)
#define PI                 3.1415926535897932385
#define Sin(a)             sin((pi*a)/180)
#define remax(a,b)         a=max(a,b)
#define remin(a,b)         a=min(a,b)
#define bitcount(x)        __builtin_popcountll(x)
#define iceil(n,x)         (((n)-1)/(x)+1)
#define flush              fflush(stdout)
#define pf                 push_front()
#define pob                pop_back()
#define ins                insert
#define mii                map<int,int> 
#define show(x)            for(auto zz:x)cout<<zz<<" ";cout<<"\n";
#define show2(x)           for(auto zz:x)cout<<zz.F<<" "<<zz.S<<"\n";
#define test()             int x;cin >> x;while(x--){solve();}
#define test2()            int x;cin >> x;for(int i=1;i<=x;i++){cout << "Case #" << i << ": ";solve();}
#define watch(x)           cout << (#x) << " is " << (x) << endl
#define scn(x)             scanf("%lld",&x)
using namespace std;


/* Mathematical Functions */
int power(int x, int y);
bool isPrime(int n);
int modInv(int a, int b);
int gcdExtended(int a, int b, int *x, int* y);
int mpower(int a, int b, int p);
bool sorted(vector<int>v, int n, int strict);

const int inf = (int)1e17;
const int N = (int)3e5 + 5;

void solve() {
	int a, b, c, d;
	cin >> a >> b >> c >> d;
	if (a > b)
		swap(a, b);
	if (c > d)
		swap(c, d);
	int ans = a * c;
	ans = max(ans, a*d);
	ans = max(ans, b*c);
	ans = max(ans, b*d);
	cout << ans << endl;
}
int32_t main() {


	FASTIO;
	clock_t start, end;
	start = clock();
	solve();
	end = clock();
	double time_taken = double(end - start) / (double)CLOCKS_PER_SEC;
	//cout << fixed << setprecision(5) << time_taken << "\n";
	return 0;

}
int modInv(int a, int m)
{
	int x, y;
	int g = gcdExtended(a, m, &x, &y);
	int res = (x%m + m) % m;
	return res;
}

int gcdExtended(int a, int b, int *x, int *y)
{
	if (a == 0) {
		*x = 0, *y = 1;
		return b;
	}
	int x1, y1;
	int gcd = gcdExtended(b%a, a, &x1, &y1);
	*x = y1 - (b / a) * x1;
	*y = x1;
	return gcd;
}

int mpower(int x, int y, int p)
{
	int res = 1;
	x = x % p;
	while (y > 0) {
		if (y & 1) res = (res*x) % p;
		y = y >> 1;
		x = (x*x) % p;
	}
	return res;
}
int power(int x, int y)
{
	int res = 1;
	while (y > 0) {
		if (y & 1) res = res * x;
		y = y >> 1;
		x = x * x;
	}
	return res;
}

bool isPrime(int n)
{
	if (n <= 1)  return false;
	if (n <= 3)  return true;
	if (n % 2 == 0 || n % 3 == 0) return false;
	int p = sqrt(n);
	for (int i = 5; i <= p; i = i + 6)
		if (n%i == 0 || n % (i + 2) == 0)
			return false;
	return true;
}
bool sorted(vector<int>v, int n, int strict) {
	if (n <= 1)
		return 1;
	for (int i = 1; i < n; i++) {
		if (strict) {
			if (v[i] <= v[i - 1])
				return 0;
		}
		else {
			if (v[i] < v[i - 1])
				return 0;
		}
	}
	return 1;
}


Measured memory_bytes: 3696