///jai sri krishna
///jai maa kali


#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace __gnu_pbds;


typedef long long ll;
typedef long double ld;
typedef tree<
ll,
null_type,
less_equal<ll>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

#define db double
#define pii pair<ll,ll>
#define f(i,a,b) for(ll i=a;i<b;i++)
#define fi(i,a,b,c) for(ll i=a;i<b;i+=c)
#define fr(i,a,b) for(ll i=a;i>=b;i--)
#define fri(i,a,b,c) for(ll i=a;i>=b;i-=c)
#define pb push_back
#define ss second
#define ff first
#define in insert
#define sq(x)  (x*x)
#define all(a)  a.begin(),a.end()
#define nl '\n'
#define npii pair<ll,ll>
#define mnpq  priority_queue <npii, vector<npii>, greater<npii> >

ll gcd(ll a,ll b){
       if(b==0)return a;
       return gcd(b,a%b);
}
int getRandom(int L,int R)
{
    return rng()%(R-L+1) + L;
}

ll lcm(ll a,ll b){
       return ((a)/gcd(a,b))*b;
}

ll bigmod(ll a,ll n,ll md){
       if(n==0){
           return 1;
       }
       if(n==1){
           return a%md;
       }
       ll d= bigmod(a,n/2,md);
       if(n%2==0){
           return (d*d)%md;
       }
       else{
           return ( ((d*d)%md) * (a%md) )%md;
       }
}

bool sortbysec(const pair<int,int> &a,
            const pair<int,int> &b)
{

    if(a.first==b.first){
         return (a.second > b.second);
    }

    return (a.first< b.first);
}


const ll  N = 200005;
const ll mod = 998244353;

const ll neginf= -1e18;
const ll inf = 1e18;
const ld eps= 1e-9;


/// Think reverse order
/// think 10 minute before submission
/// wrong submission have 20 minute penalty
/// use binary search for maximum minimum problem
/// use broute force to check test case in another solution



int main(){

       ios_base::sync_with_stdio(false);
       cin.tie(NULL);
       cout.tie(NULL);

       vector<ll>v;
       f(i,0,4){
         ll a;
         cin>>a;
         v.pb(a);
       }

       sort(all(v));

       cout<<v[0]*v[2];


}