//Code by Patcas Csaba

#include <vector>
#include <string> 
#include <set> 
#include <map> 
#include <queue> 
#include <bitset> 
#include <stack>
#include <list>

#include <numeric> 
#include <algorithm> 

#include <cstdio>
#include <fstream>
#include <iostream> 
#include <sstream> 
#include <iomanip>

#include <cctype>
#include <cmath> 
#include <ctime>
#include <cassert>

using namespace std;

#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >

#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REPEAT do{ 
#define UNTIL(x) }while(!(x)); 

#define SZ size()
#define BG begin() 
#define EN end() 
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()

#define in_file "a.in"
#define out_file "a.out"

VI a;

int main()
{
	//Read data
	//freopen(in_file, "r", stdin);
	//freopen(out_file, "w", stdout);
	
	a.RS(4);
	cin >> a[0] >> a[1] >> a[2] >> a[3];
	int sol = 0;
	sort(ALL(a));

	do {
		int ans = a[0] * a[1] + a[2] * a[3];
		sol = max(sol, ans);
	} while (next_permutation(ALL(a)));

	//Solve
	cout << sol;

	//Write data


	return 0;
}