/*
	katana_handler
	My best submission yet for problem B - https://codeforces.com/contest/754/submission/23605202
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set_pll tree <pll, null_type,less<pll>, rb_tree_tag,tree_order_statistics_node_update>
#define ordered_set tree <ld, null_type,less<ld>, rb_tree_tag,tree_order_statistics_node_update>
//query 1 order_of_key (k) : Number of items strictly smaller than k .
//query 2 find_by_order(k) : K-th element in the set (counting from zero).
//less<ll> means query 1 will return numbers strictly less than k
//greater<ll> means query 1 will return numbers strictly greater than k
#define        pb                push_back
#define        pf                push_front
#define        MOD                1000000007
#define        popb            pop_back
#define        popf            pop_front
#define        len(x)            (ll)x.size()    
#define        MAXN            100001
#define        mp                make_pair
#define        endl            '\n'
#define        ff                first
#define        ss                second
#define        tt                third
#define        mapcl            map<char,ll>
#define        mapll            map<ll,ll>
#define        cmp                complex<double>
#define        pi                3.141592653589793238462643383279502884197169399375105820974944592307816406286
#define        inf                LLONG_MAX
#define        flush            fflush(stdout)
#define        vll                vector<ll>
#define        all(v)            v.begin(),v.end()
#define        fr(i,z,n)        for(ll i=z;i<n;i++)
#define        sqrt            sqrtl
#define        cbrt            cbrtl
typedef        long long        ll;
typedef        pair<ll,ll>        pll;
typedef        long double        ld;
ll             power(ll a,ll b,ll mod)            {if(b==0)return 1;ll tmp=power(a,b/2,mod);tmp=(tmp*tmp)%mod;if(b&1)tmp=(tmp*a)%mod;return tmp;}
ll             mandist(pll a,pll b)            {return abs(a.ff-b.ff)+abs(a.ss-b.ss);}
ld            dist2d(pll a,pll b)                {ll x=abs(a.ff-b.ff);ll y=abs(a.ss-b.ss);return (sqrt((x*x)+(y*y)));}
bool        coll(pll p1,pll p2,pll p3)        {if((p3.ss-p2.ss)*(p2.ff-p1.ff)==(p2.ss-p1.ss)*(p3.ff-p2.ff))return true;else return false;}
void        print(auto x)                    {cout<<x<<endl;}
void        pv(vector<auto> v)                {for(ll i=0;i<(ll)v.size();i++)cout<<v[i]<<" ";cout<<endl;}
void        pv1(vector<auto> v)                {for(ll i=1;i<(ll)v.size();i++)cout<<v[i]<<" ";cout<<endl;}
void        pset(set<auto> v)                {for(auto x:v)cout<<x<<" ";cout<<endl;}
void        pvsl(vector<auto> v)            {for(ll i=0;i<(ll)v.size();i++)cout<<v[i]<<" ";}
void        in(vector<auto> &v, ll n)        {v.resize(n);for(ll i=0;i<n;i++)cin>>v[i];}
void        in1(vector<auto> &v, ll n)        {v.resize(n+1);for(ll i=1;i<=n;i++)cin>>v[i];}
void        sorta(auto &v)                    {sort(v.begin(),v.end());}
void        sortd(auto &v)                    {sort(v.begin(),v.end(),greater <>());}		
void        fast()                            {ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);}
//all variables and functions below this line
void solve()
{
	ll a,b,c,d;
	cin>>a>>b>>c>>d;
	cout<<max(max(a*c,a*d),max(b*c,b*d))<<endl;
}
int main()
{
	//srand(time(NULL));
	fast();
	ll t=1;
	//cin>>t;
	for(ll i=1;i<=t;i++)
	{
		//cerr<<t<<endl;
		//cout<<"Case #"<<i<<": ";
		solve();
	}
}


Measured memory_bytes: 3692