#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

int main(){
	int n;
	vector <int> a;
	//freopen("input.txt", "r", stdin);
	for(int i = 0; i < 4; ++i){
		cin >> n;
		a.push_back(n);
	}
	sort(a.begin(), a.end());
	cout << a[0] * a[1] + a[2] * a[3];
	return 0;
}