#define _GLIBCXX_DEBUG

#include <bits/stdc++.h>
using namespace std;
#define vec vector
#define fi first
#define se second
#define eb emplace_back
#define ef emplace_front
#define pof pop_front()
#define pob pop_back()
#define mp make_pair
#define Rep(i,n) for(li i=0,nn=(li)(n);i!=nn;++i)
#define Rep1(i,n) for(li i=1,nn=(li)(n)+1;i!=nn;++i)
#define rRep(i,n) for(li i=n-1;i>=0;--i)
#define rRep1(i,n) for(li i=n;i>=1;--i)
#define each(x,v) for(auto x:v)
#define eachitr(it,v) for(auto it=v.begin();it!=v.end();++it)
#define eachritr(it,v) for(auto it=v.rbegin();it!=v.rend();++it)
#define Size(v) (li)(v.size())
#define SortA(v) sort(v.begin(),v.end())
#define SortD(v) sort(v.rbegin(),v.rend())
#define All(a) (a).begin(),(a).end() 
#define input(a) for(li ii=0,nn=(li)(a.size());ii!=nn;++ii){cin>>(a).at(ii);}
#define input2(a,b) for(li ii=0,nn=(li)(a.size());ii!=nn;++ii){cin>>(a).at(ii)>>(b).at(ii);}
using li = int64_t;
using intl = int64_t;
using ld = long double;
using vi = vec<li>;
using vb = vec<bool>;
using vd = vec<ld>;
using vvi = vec<vi>;
using qi = deque<li>;
using vqi = vector<qi>;
using pqi = priority_queue<li>;
using pi = pair<li, li>;
using vpi = vec<pi>;
using si = set<li>;
using vsi = vec<si>;
using mii = map<li, li>;
using vmii = vec<mii>;
vec<li> dx = {0, 1, 0, -1, 1, 1, -1, -1};
vec<li> dy = {1, 0, -1, 0, 1, -1, 1, -1};
constexpr li INF = LLONG_MAX;

template<class T>bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }

void Yes(bool b) {
	if (b)cout << "Yes";
	else cout << "No";
}
void yes(bool b) {
	if (b)cout << "yes";
	else cout << "no";
}
void YES(bool b) {
	if (b)cout << "YES";
	else cout << "NO";
}

queue<string> argment_contents;
void set_args_con() {}
template<class First, class... Rest>
void set_args_con(const First& first, const Rest&... rest) {
    stringstream ss;
    ss<<first;
    argment_contents.push(ss.str());
    set_args_con(rest...);
}
string gen_string(string s) {
    s+=',';
    string ret="";
    int par=0;
    for(int i=0; i<(int)s.size(); i++) {
        if(s[i]=='(' || s[i]=='<' || s[i]=='{') par++;
        else if(s[i]==')' || s[i]=='>' || s[i]=='}') par--;
        if(par==0 && s[i]==',') {
            ret+="="+argment_contents.front();
            argment_contents.pop();
            if(i!=(int)s.size()-1) {
                ret+=",";
            }
        }
        else ret+=s[i];
    }
    return ret;
}
#define dump(...) {set_args_con(__VA_ARGS__);cerr<<gen_string(#__VA_ARGS__)<<endl;}



/* //__int128用
using lli = __int128;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
  std::ostream::sentry s(dest);
  if (s) {
    __uint128_t tmp = value < 0 ? -value : value;
    char buffer[128];
    char *d = std::end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (value < 0) {
      --d;
      *d = '-';
    }
    int len = std::end(buffer) - d;
    if (dest.rdbuf()->sputn(d, len) != len) {
      dest.setstate(std::ios_base::badbit);
    }
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
    if ('0' <= s[i] && s[i] <= '9')
      ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

/* //mod用
constexpr li mod = 1000000007;

intl modpow(intl a, intl n, intl p){
  intl res = 1;
  while (n > 0){
    if (n&1){res = (res * a) % p;}
	a = (a * a) % p;
    n >>= 1;
  }
  return res;
}

intl modinv(intl a, intl p){
  if (a == 0){
    cout << "/0 at modinv"<<endl;
    exit(0);
  }
  if (a < 0){
    cout << "/- at modinv" <<endl;
    exit(0);
  }
  if (a==1){return 1;}
  if (a > p){return modinv(a%p, p);}

  return p - ( modinv(p%a,p) * (p/a) ) % p;
}

intl modcomb(intl n, intl k, intl p){
  if (k > n || k < 0 || n < 0){
    cout << "error at modcomb"<<endl;
    exit(0);
  }
  if (2*k > n){ k = n-k;}
  if (k ==0){return 1;}
  intl c=1;
  for (intl i = 0; i < k; i++){
    c =( c * ( (n-i) % p ) % p ) * modinv(i+1,p) % p;
  }
  return c;
}
*/



int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
	cout.precision(16);

	vi a(2),c(2);

	input(a);input(c);

	li maxa=-1*INF;

	each(x,a){
		each(y,c){
			chmax(maxa,x*y);
		}
	}

	cout<<maxa;







}

Measured memory_bytes: 3688