#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>

using namespace std;

int main()
{
	vector<int> numbers;
	for(int i = 0; i < 4; i++)
	{
		int temp = 0;
		cin >> temp;
		numbers.push_back(temp);
	}
	sort(numbers.begin(), numbers.end());
	cout << (numbers[3] * numbers[2]) + (numbers[1] * numbers[0]) << endl;
	return 0;
}