#include <bits/stdc++.h>
using namespace std;

#define pb(a) push_back((a))
#define mp(a, b) make_pair((a), (b))
#define REP(a, b) for (ll i = (a); i < (b); i++)
#define REP2(a, b) for (ll j = (a); j < (b); j++)
#define REPE(a, b, c, d) \
    REP(a, b)            \
    for (ll j = (c); j < (d); j++)
#define REPV(a, b, c) for (ll(a) = b; (a) < (c); (a)++)
#define IREP(a, b) for (ll i = (a); i >= (b); i--)
#define IREP2(a, b) for (ll j = (a); j >= (b); j--)
#define IREPV(a, b, c) for (ll(a) = b; (a) >= (c); (a)--)
#define all(v) (v).begin(), (v).end()
#define trvs(c) for (auto &it : c)
#define INF 1e18
#define sz(x) (long long)(x.size())
#define flash                         \
    ios_base::sync_with_stdio(false); \
    cin.tie(0);                       \
    cout.tie(0);
#define F first
#define S second
#define MOD 1000000007

using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using vvpll = vector<vpll>;
#define _DEBUG 1
#if _DEBUG
#define debug(x) cout << #x << "=" << x << endl
#define debug2(x, y) cout << #x << "=" << x << " " << #y << "=" << y << endl;
#define debug3(x, y, z) cout << #x << "=" << x << " " << #y << "=" << y << " " << #z << "=" << z << endl;
#define debug4(x, y, z, w) cout << #x << "=" << x << " " << #y << "=" << y << " " << #z << "=" << z << " " << #w << "=" << w << endl;
#define debug5(x, y, z, w, t)      \
    cout << #x << "=" << x << " "; \
    debug4(y, z, w, t);
#define debug6(p, x, y, z, w, t)                            \
    cout << #p << " " << p << " " << #x << "=" << x << " "; \
    debug4(y, z, w, t);
#define debug7(o, p, x, y, z, w, t) \
    cout << #o << " " << o << " ";  \
    debug6(p, x, y, z, w, t);
#define wait  \
    int xxxx; \
    cin >> xxxx;
#define derr(x) cerr << #x << "=" << x << endl;
#define derr2(x, y) cerr << #x << "=" << x << " " << #y << "=" << y << endl;
#define derr3(x, y, z) cerr << #x << "=" << x << " " << #y << "=" << y << " " << #z << "=" << z << endl;
#define derr4(x, y, z, w) cerr << #x << "=" << x << " " << #y << "=" << y << " " << #z << "=" << z << " " << #w << "=" << w << endl;
#define derr5(x, y, z, w, t)       \
    cerr << #x << "=" << x << " "; \
    derr4(y, z, w, t);
#define derr6(p, x, y, z, w, t)                             \
    cerr << #p << " " << p << " " << #x << "=" << x << " "; \
    derr4(y, z, w, t);
#define derr7(o, p, x, y, z, w, t) \
    cerr << #o << " " << o << " "; \
    derr6(p, x, y, z, w, t);
ll checkpoint_counter = 0;
#define checkpoint cerr << "At checkpoint : " << checkpoint_counter++ << endl;

#else
#define debug(x) ;
#define debug2(x, y) ;
#define debug3(x, y, z) ;
#define debug4(x, y, z, q) ;
#define debug5(x, y, z, r, t) ;
#define debug6(x, y, z, r, t, s) ;
#define debug7(x, y, z, r, t, s, u) ;
#define wait ;
#define derr(x) ;
#define derr2(x, y) ;
#define derr3(x, y, z) ;
#define derr4(x, y, z, q) ;
#define derr5(x, y, z, r, t) ;
#define derr6(x, y, z, r, t, s) ;
#define derr7(x, y, z, r, t, f, u) ;
#define checkpoint ;
#endif

#define print_matrix(a, n, m) \
    REPE(0, n, 0, m) { cout << (a)[i][j] << ((j == m - 1) ? '\n' : ' '); }
#define present(container, element) (container.find(element) != container.end())
#define endl "\n"

// auto cmp = [](pair<ll, pair<ll, ll>> a, pair<ll, pair<ll, ll>> b) {
//     if (a.F == b.F)
//         return a.S.F > b.S.F;
//     return a.F > b.F;
// };
//decltype(cmp)
// set.count(x)==0 not present
// accumulate (all(a),sum) or accumulate(all(a),sum,myfunc)
//partial_sum(all(a),b)   a and b are vectors puts prefix array of a in b
// partial_sum(all(a),b,myfunc)
//g++ -std=c++17 .\ans.cpp | ./a.exe
bool cmp(ll a, ll b){
    if(abs(a)==abs(b)){
        return a>b;
    }
    return abs(a)>abs(b);
}
void solve()
{
    ll a,b,c,d;
    cin>>a>>b>>c>>d;
    cout<<max({a*c,a*d,b*c,b*d})<<endl;
}

int main()
{
    flash


    ll t;
    // cin >> t;
    // while (t--)
    solve();
    cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";
    return 0;
}

Measured memory_bytes: 3800