#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;

int main() {
	int a, b, c, d;
	vector<int> v;
	cin >> a >> b >> c >> d;
	v.push_back(a);
	v.push_back(b);
	v.push_back(c);
	v.push_back(d);
	sort(v.begin(), v.end());
	cout << v[0] * v[1] + v[2] * v[3];
	return 0;
}