///   BISMILLAHIR RAHMANIR RAHEEM
///   ALLAH IS WATCHING ME
///   ALLAH save us from COVID-19.Amin.

///   Every soul shall taste death.

///   Tag ::

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>


///  order_of_key return number of elements less than x.
///  find_by_order return index.
using namespace std;
using namespace __gnu_pbds;


#define MOHAMMAD  ios::sync_with_stdio(0);cin.tie(0);
#define all(x)    (x).begin(), (x).end()
#define AE        cout << fixed << setprecision(2);


/// faster.
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")

int dx8[] = {0, 0, 1, 1, 1, -1, -1, -1}; // 8-direction.......
int dy8[] = {1,-1, 1, -1, 0, 0, -1, 1};
int dx4[]= {1,-1,0,0}; // 4-direction...........
int dy4[]= {0,0,1,-1};

using ll = long long;
const ll MOD = 1e9 + 7;

typedef tree< int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef tree<pair<int, int>,null_type,less<pair<int, int>>,rb_tree_tag,tree_order_statistics_node_update> ordered_multiset;

//debug
template<typename F,typename S>ostream&operator<<(ostream&os,const pair<F,S>&p){return os<<"("<<p.first<<", "<<p.second<<")";}
template<typename T>ostream&operator<<(ostream&os,const vector<T>&v){os<<"{";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<*it;}return os<<"}";}
template<typename T>ostream&operator<<(ostream&os,const set<T>&v){os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<",";os<<*it;}return os<<"]";}
template<typename T>ostream&operator<<(ostream&os,const multiset<T>&v) {os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<*it;}return os<<"]";}
template<typename F,typename S>ostream&operator<<(ostream&os,const map<F,S>&v){os<<"[";for(auto it=v.begin();it!=v.end();++it){if(it!=v.begin())os<<", ";os<<it->first<<" = "<<it->second;}return os<<"]";}
#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)
void faltu(){cerr << endl;}
template<typename T>void faltu(T a[],int n){for(int i=0;i<n;++i)cerr<<a[i]<<' ';cerr<<endl;}
template<typename T,typename...hello>void faltu(T arg,const hello&...rest){cerr<<arg<<' ';faltu(rest...);}
//#else
//#define dbg(args...)

/// Modular arithmetic
inline void normal(ll &a) { a %= MOD; (a < 0) && (a += MOD); }
inline ll modMul(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a*b)%MOD; }
inline ll modAdd(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a+b)%MOD; }
inline ll modSub(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); a -= b; normal(a); return a; }
inline ll modPow(ll b, ll p) { ll r = 1; while(p) { if(p&1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }
inline ll modInverse(ll a) { return modPow(a, MOD-2); }  /// When MOD is prime.
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }

//***********************************************  The END **********************************************************************************************************************************
const ll N = 1e5;
const ll INF = 1e18;
const ll limit = (1LL<<64) - 1;


int main()
{

   MOHAMMAD

   ll a , b , c , d;
   cin >> a >> b >> c >> d;
  // if ( a>b ) swap( a , b );
  // if ( c>d ) swap ( c , d );
   ll mx = a*c;
   mx = max ( mx , b * d );
   if ( (a<=0 and b>=0) or ( c<=0 and d>=0 ) ) mx = max ( mx , 0LL );
   mx = max ( mx , a*d );
   mx = max ( mx , b*c );

   cout << mx << "\n";


}



/*
Explanation:





----------------------------------------------------------------------------------------------------------------

Topic    :: Bellman-Ford Algorithm
Practice ::

  1. https://open.kattis.com/problems/allpairspath
  2. https://www.spoj.com/problems/SEGMENTS/
  3. https://cses.fi/problemset/task/1673
  4. https://cses.fi/problemset/task/1197
  5.

Topic    :: Centroid Decomposition.
Practice ::
  1.
  2.
  3.
  4.
  5.


  Alhamdulillah
*/


Measured memory_bytes: 3648