//ABHISHEK AGRAWAL,BIT mesra//                    
                      //Newbie......You have to be odd to be no. ONE :)//
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define ld long double
#define fl float
#define lcm(a,b) (a*(b/__gcd(a,b)))
#define vs vector <string>
#define vc vector <char>
#define vii vector<int>
#define vll vector<ll>
#define sll set<ll>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define plc pair<ll,char>
#define tlll tuple<ll,ll,ll>
#define mt make_tuple
#define vpll vector<pair<ll,ll>>
#define vpii vector<pair<int,int>>
#define vtll vector<tuple<ll,ll,ll>>
#define vvll vector<vector<ll>>
#define lb lower_bound
#define pb push_back
#define pob pop_back
#define f first
#define s second
#define mll map<ll,ll>
#define mp make_pair
#define sp(n) fixed<<setprecision(n)
#define mcl map<char,ll>
#define msl map<string,ll>
#define mod (ll)1000000007
#define flash ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL); 
#define test ll t;read(t);while(t--) 
#define sortv(v) sort(v.begin(),v.end())
#define INF (ll)(1e15)
#define loop(i,n) for(int i=0;i<n;i++)
#define loop1(i,n) for(int i=1;i<=n;i++)
#define rloop(n,i) for(int i=n-1;i>=0;i--)
#define loopab(i,a,b,c) for(int i=a;i<=b;i+=c)
#define reada(a,n) loop(i,n) cin>>a[i];
#define reada1(a,n) loop1(i,n) cin>>a[i];
#define sorta(a) sort(a,a+n,greater<ll>())
#define countone(n) __builtin_popcount(n)
#define numoftrailzero(n) __builtin_ctz(n)
#define maxpowoftwo(n) __builtin_clz(n)
#define leastindexwithone(n)  __builtin_ffs(n)
#define what_is(x) cerr << #x << " is " << x << endl;
#define pfv(v) cout<<v.size()<<"\n";loop(i,v.size()) cout<<v[i]<<" ";cout<<"\n";
#define pv(v) loop(i,v.size()) cout<<v[i]<<" ";
#define all(v) v.begin(),v.end()
#define mset(dp,val) memset(dp,val,sizeof(dp))
//if we need to devide any given number in powers of term the power of max term
#define answer(n) ceil(log2(n+1))
   int q;ll n;ll ans,sum;
// ll gcd(ll a, ll b){if (b==0){return a;} return gcd(b,a%b);}
 ll powe(ll a,ll b){ll res=1;while(b>0){if(b%2 ==1){res=(res*a);}a=(a*a);b/=2;} return res;}
// ll power(ll a,ll b,ll M){a%=M;ll res=1;while(b>0){if(b%2 ==1){res=(res*a)%M;}a=(a*a)%M;b/=2;} return res;}
// ll extendedEuclid(ll A,ll B,ll &x,ll &y){
//     if(B == 0) {
//         x = 1;
//         y = 0;
//         return A;
//     }
//     else {
//         ll x1 , y1;
//         ll gcd = extendedEuclid(B,A%B,x1,y1);
//         y = x1-(A/B)*y1; 
//         x = y1;
//         return gcd;
//     }
// }
// ll mi(ll A, ll M){ll x,y;extendedEuclid(A,M,x,y);if(x<0){x+=mod;} return x;}
// vector<bool>sieve(1000000,true);
// void Sieve(){
//  sieve[0]=false;
//  sieve[1]=false;
//  for(ll i=2;i*i<=1000000;i++){
//   if(sieve[i]==true){
//    for(ll j=i*i;j<1000000;j+=i)
//     sieve[j]=false;
//   }
//  }
// }
//  vll sieve_spf;
// void Sieve_spf(){
//  const ll n = 1e6 + 5;
//  sieve_spf.resize(n);
 
//  loop(i,n)
//   sieve_spf[i]=i;
 
//  sieve_spf[0]=-1;
//  sieve_spf[1]=1;
 
//  loopab(i,2,n,2)
//   sieve_spf[i]=2;
 
//  loopab(i,3,n,2)
//   if(sieve_spf[i]==i)
//    loopab(j,i*i,n,i)
//     if(sieve_spf[j]==j)
//      sieve_spf[j]=i;
// }
// #ifdef TESTING 
// #define DEBUG fprintf(stderr, "====TESTING====\n") 
// #define VALUE(x) cerr << "The value of " << #x << " is " << x << endl 
// #define debug(...) fprintf(stderr, __VA_ARGS__) 
// #else 
// #define DEBUG 
// #define VALUE(x) 
// #define debug(...) 
// #endif
// bool isUpcase(char c){
//     if(c >= 'A'&&c <= 'Z') return true;
//     else return false;
// }
// bool islowcase(char c){
//     if(c >= 'a'&&c <= 'z') return true;
//     else return false;
// }
void the_happiest_place_on_earth()
{
    flash;
  #ifdef ENABLE_FILE_IO
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
  #endif      
} 
// bool comp(const pii &a, const pii &b){
//  if(a.f<b.f&&a.s>=0&&b.s>=0)
//   return true;
//  else if(a.s<0&&b.s<0&&a.f+a.s>b.f+b.s)
//   return true;
//  else
//   return false;
// }

const int N=1900055;ll b[N],a[N],dis[N],par[N];
vii graph[N];bool vis[N];
// bool vis[N];mll m1;
// map<pii,int>k;
// void gra(ll m){
//   loop(i,m){
//     ll x,y,w;cin>>x>>y>>w;
//     x--,y--;
//     graph[x].pb({y,w});
//     graph[y].pb({x,w});
//   }
// }
// ll cnt;int val[N]={0};
void dfs(int node,int pa){
  vis[node]=true;
  par[node]=pa;
  for(int x:graph[node]){
    if(!vis[x]){
      dfs(x,node);
    }
  }
  //order.pb(node);
}
// void dfs1(int node,int c){
//   vis[node]=true;
//   cmp[node]=c;
//   for(int x:graph1[node]){
//     if(!vis[x]) dfs1(x,c);
//   }
// }
ll t;
void testcase(){
  ll a,b,c,d; 
  cin>>a>>b>>c>>d;
  ans=max({a*c,a*d,b*c,b*d});
  cout<<ans;
  return;
}

int main(){
  //the_happiest_place_on_earth;
  //Today's thought: Push yourself,because no one else is going to do it for you.
  //Things aren’t always #000000 and #FFFFFF
  //START OF PROGRAM LOGIC
  //g++ -o a BB.cpp -DENABLE_FILE_IO;./a
  the_happiest_place_on_earth();
  // dp[0]=1;
  // loop1(i,N){
  //   dp[i]=dp[i-1]*i;
  //   dp[i]%=mod;
  // }
  q=1;
  //cin>>t>>q;   
  while(q--){
    //cout<<"Case #"<<++t<<": ";
    testcase();
  } 
  cerr << "Time : " << 1000 *((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";
  //END OF PROGRAM LOGIC
	return 0;
}
/*
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*/

Measured memory_bytes: 48328