#pragma GCC optimize("Ofast")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <iostream>
#include <list>
#include <algorithm>
#include <map>
#include <math.h>
#include <set>
#include <string>
#include <algorithm>
#include <cstdint>
#include <list>
#include <string.h>
#include <unordered_map>
#include <assert.h>
#include <ctype.h>
#include <queue>
#include <numeric>
#include <vector>
#include <iomanip>
#include <deque>
#include <cstdlib>
#include <stack>
#include <ctime>
#define  lld  long long int
#define newline cout << endl
#define pb push_back
#define mp make_pair
lld shouldendl = 1;
#define se second
#define fi first
#define sfind(s,ele) (s).find((ele));
#define SPEED ios:: sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define starttime chrono::time_point<chrono::system_clock> start, end; start = chrono::system_clock::now()
#define showtime end = chrono::system_clock::now();  chrono::duration<double> elapsed_seconds = end - start; time_t end_time = chrono::system_clock::to_time_t(end); cout << "elapsed time: " << elapsed_seconds.count() << "s\n"
lld  INF = (lld)(5e17+100);
lld MOD =  (lld)(1e18+100);
#define fileopen   freopen("input.txt", "rt", stdin); freopen("output.txt", "wt", stdout);
using namespace std;
lld modInverse(lld a ){   lld m = MOD,m0 = m, y = 0, x = 1;  if (m == 1) return 0;   while (a > 1) {  lld q = a / m, t = m;  m = a % m, a = t, t = y;          y = x - q * y, x = t;   } if (x < 0)  x += m0; return x; } 
lld add(long long a, long long b){return ((a%MOD)+(b%MOD))%MOD;}
lld mul(long long a, long long b){return ((a%MOD)*(b%MOD))%MOD;}
lld sub(long long a, long long b){lld ans = ((a%MOD-b%MOD))%MOD; if(ans<0) ans += MOD; return ans;}
lld gcd(lld a, lld b){if (b == 0) return a; return gcd(b, a % b);}
void MAIN(lld i,lld t);
int get(){lld t;cin>>t; ; return t;}
template<class T> int logd(T name){cout<<name<<endl; return 0;}
void test(int t) { for(lld i = 1;i<=t;i++){MAIN(i,t); if(shouldendl) cout << endl; } }
lld power(lld x, lld y) { lld res = 1; x = x%MOD; if(x==0) return 0;   while (y > 0) {   if (y & 1)      res = (res*x)%MOD; y = y>>1; x = (x*x)%MOD;} return res; }
template <typename T,typename U> std::pair<T,U> operator+(const std::pair<T,U> & l,const std::pair<T,U> & r) {   return {l.first+r.first,l.second+r.second};                                    }    
#define all(v) (v).begin(),(v).end()
lld popcount(lld x){return __builtin_popcountll(x);}
lld lcm(lld a,lld b){ return (a*b)/gcd(a,b);}
template<class T> bool input(vector<T> &v, lld n = -1){ assert(v.size()!=0); if(n==-1) n = v.size();    for(auto &i:v) cin >> i; return 0;}
template<class T> bool print(vector<T> v,lld l = 0, lld r = -1){  if(r==-1) r = v.size();   for(int i = l;i<r;i++) cout << v[i] << " "; return 0;}
//Observation, binary_search, dfs on strings, simplify the problem
//Observe and ELIMINATE 
void MAIN(lld current_test_case,lld total_test_cases){ 
     lld a,b,c,d;
     cin >> a >> b >> c >> d;

    cout << max(max(max(min(a,b)*max(c,d),min(c,d)*max(a,b)),max(c,d)*max(a,b)),min(a,b)*min(c,d));
     
}     
int main(){  
    SPEED;
    #ifndef ONLINE_JUDGE 
     fileopen
    #endif
    test(1);
    return 0;
}


Measured memory_bytes: 3232