//I am so vegetable
//#define err
#pragma GCC optimize(2)
#include <bits/stdc++.h>
#define FIO ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#define POB pop_back
#define PUB push_back
#define IN insert
#define ER erase
#define CT count
#define EP empty
#define FI first
#define SE second
#define lsi p<<1
#define rsi p<<1|1
#define lson l,m,lsi
#define rson m+1,r,rsi
#define BE 1,n,1
#define _for(i,a,b) for(int i = (a);i<(b);++i)
#define _rfor(i,a,b) for(int i = (a);i>(b);--i)
#define _sfor(p,st) for(auto &p:st)
#define endl '\n'
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int inf = 0x3f3f3f3f;
const int MOD = 1e9+7;
const double eps = 1e-6;
const double pi = acos(-1.0);
ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll qpow(ll x, ll y) { ll ans = 1; for (; y > 0; y >>= 1) { if (y & 1)ans *= x; x *= x; }return ans; }
ll qpow(ll x, ll y, int MOD) { ll ans = 1; for (; y > 0; y >>= 1) { if (y & 1)ans = ans*x%MOD; x = x*x%MOD; }return ans; }
void exgcd(ll a,ll b,ll &x,ll &y){
    if(!b){x=1;y=0;return;}
    exgcd(b,a%b,x,y);
    ll X=x;
    x=y; y=X-a/b*y;
}
ll inv(ll x, int mod = MOD) { return qpow(x, mod - 2,mod); }
ll m_m(ll a){ return (a%MOD+MOD)%MOD; }


signed main() {
  //ifstream cin("E:\\acm dream\\in.in");
  //ofstream cout("E:\\acm dream\\out.out");
  FIO;
  #ifdef err
  double be = clock();
  #endif

  ll a,b,c,d;cin>>a>>b>>c>>d;
  ll ans = max(a*c,max(a*d,max(b*c,b*d)));
  if(a<=0&&b>=0||c<=0&&d>=0)ans=max(0ll,ans);
  cout<<ans;

  #ifdef err
  double en = clock();
  cout<<"time: "<<fixed<<setprecision(8)<<en-be;
  #endif
  return 0;
}
/*                                                                                                                
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*/

Measured memory_bytes: 3652