#include <bits/stdc++.h>
using namespace std;

#define ll long long int
#define ld long double
#define endl "\n" 

// loops here
#define f(i,n) for(int i=0;i<n;i++)
#define f1(i,n) for(int i=1;i<n;i++)
#define rf(i,n) for(int i=n-1;i>=0;i--)
#define fab(i,a,b) for(int i=a;i<b;i++)
#define rfab(i,a,b) for(int i=a;i>=b;i--)

#define mod 1000000007
#define maxi INT_MAX

// input here
#define c(x) ll x;cin>>x
#define cc(x,y) ll x,y;cin>>x>>y
#define ccc(x,y,z) ll x,y,z; cin>>x>>y>>z
#define cv(v,n) for(ll i=0;i<n;i++){ll e;cin>>e;v.push_back(e);}
#define ca(a,n) for(ll i=0;i<n;i++){cin>>a[i];}

// vector here
#define pb push_back
#define vll vector<ll>
#define vchar vector<char>
#define vstr vector<string>
#define vvll vector<vll>
#define vint vector<int>
#define pll pair<ll,ll>
#define vpair vector<pll>
#define mp(x,y) make_pair(x,y)
#define pii pair<int,int>
#define fi first
#define se second

// stl func here
#define bs(a,n) binary_search(all(a),n)
#define lb(a,n) lower_bound(all(a),n)
#define ub(a,n) upper_bound(all(a),n)
#define dist(a,it) std::distance(a.begin(),it)
#define adv(it,n) std::advance(it, n)
#define all(a) a.begin(),a.end()
#define mx(a) *max_element(all(a))
#define mn(a) *min_element(all(a))

#define err() cout<<"==================================\n";
#define errA(A) for(auto i:A)   cout<<i<<" ";cout<<"\n";
#define err1(a) cout<<#a<<" "<<a<<"\n"
#define err2(a,b) cout<<#a<<" "<<a<<" "<<#b<<" "<<b<<"\n"
#define err3(a,b,c) cout<<#a<<" "<<a<<" "<<#b<<" "<<b<<" "<<#c<<" "<<c<<"\n"
#define err4(a,b,c,d) cout<<#a<<" "<<a<<" "<<#b<<" "<<b<<" "<<#c<<" "<<c<<" "<<#d<<" "<<d<<"\n"


auto clk = clock();

// // Functions 

//  // largest power of 2 less than or equal to given nobr
// ll largest_power(ll N){ N = N | (N >> 1);N = N | (N >> 2);N = N | (N >> 4);N = N | (N >> 8);
// return (N + 1) >> 1;
// }

// // sort vector of pair by second value
// bool sortbysec(const pair<ll, ll> &a, const pair<ll, ll> &b){
//     return (a.second < b.second);
// }
 
// #define MAXN 100001 
// ll spf[MAXN];
 
// // Function to Calculate smallest prime factor (spf) of first MAXN natural numbers
// void sieve() { 
//     spf[1] = 1; for (ll i=2; i<MAXN; i++) spf[i] = i; for (ll i=4; i<MAXN; i+=2) spf[i] = 2; 
//     for (ll i=3; i*i<MAXN; i++) if (spf[i] == i) for (ll j=i*i; j<MAXN; j+=i) if (spf[j]==j) spf[j] = i; 
// } 
 
// // Function to get factorization of a number (uncomment sieve function and declaration of spf, MAXN)
// vector<ll> getFactorization(ll x) {
//     vector<ll> ret; while (x != 1) { ret.push_back(spf[x]); x = x / spf[x]; } return ret; 
// }
 
// // Function to Check whether a number is prime
// bool isPrime(ll n) { 
//     if (n <= 1) return false; if (n <= 3) return true; if (n % 2 == 0 || n % 3 == 0) return false; 
//     for (ll i = 5; i * i <= n; i = i + 6)  if (n % i == 0 || n % (i + 2) == 0) return false; return true; 
// } 
 
// // Function to Calculate a^b
// ll power(ll a, ll b) {
//     ll res = 1; while (b > 0) { if (b & 1) res = (res * a); a = (a * a); b >>= 1;} return res;
// }
 
// // Function to Calculate a^b % mod
// ll modpow(ll a, ll b,ll x) {
//     ll res = 1; while (b > 0) { if (b & 1) res = (res * a)%x; a = (a * a)%x; b >>= 1;} return res;
// }
 
// // Returns n^(-1) mod p (uncomment modpow function to use)
// ll modInverse(ll n, ll p) { 
//     return modpow(n, p - 2, p); 
// }   
 
// // Returns nCr % p using Fermat's little theorem. (uncomment above modInverse, modpow functions to use) 
// ll nCrModPFermat(ll n, ll r,ll p) { 
//     if (r == 0) return 1; 
//     ll fac[n + 1]; 
//     fac[0] = 1; 
//     for (ll i = 1; i <= n; i++) fac[i] = (fac[i - 1] * i) % p; 
//     return (fac[n] * modInverse(fac[r], p) % p * modInverse(fac[n - r], p) % p) % p; 
// } 
 
// // Returns nCr
// ll nCr(ll n,ll r) { 
//     ll p = 1, k = 1; 
//     if (n - r < r) r = n - r; 
//     if (r != 0) { 
//         while (r) { 
//          p *= n; k *= r; 
//             ll m = __gcd(p, k); 
//             p /= m; k /= m; n--; r--; 
//         } 
//    } 
//     else p = 1; 
//     return p; 
// }

// //modular operations

// //uncomment modpow function to use
// ll divide(ll a,ll b,ll m) {
//     return (a % m) * modpow(b, m - 2) % m;
// }

// ll mul(ll a,ll b,ll m) {
//     return ((a % m) * (b % m)) % m;
// }

// ll add(ll a,ll b,ll m) {
//     return (a % m + b % m) % m;
// }




int main()
{
    #ifndef ONLINE_JUDGE 
    freopen("input.txt", "r", stdin); 
    freopen("output.txt", "w", stdout); 
    #endif
  
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
    cout<<fixed<<setprecision(8);

   
   cc(a,b);
   cc(x,y);
  
    ll p1=b*y;
    ll p2=b*x;
    ll p3=a*y;
    ll p4=a*x;
    ll m1=max(p1,p2);
    ll m2=max(p3,p4);
    ll m=max(m1,m2);
    if(b>=0 && a<=0 || x<=0 && y>=0)
    {
    ll p5=0;
    m=max(m,p5);
    }

    cout<<m<<endl;
    #ifndef ONLINE_JUDGE
    cout << endl << "Time elapsed: " << (double)(clock() - clk) / CLOCKS_PER_SEC << endl;
    #endif

    return 0;
}

Measured memory_bytes: 3636