#include <bits/stdc++.h>

using namespace std;

#define x first
#define y second
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef long long ll;
typedef unsigned long long ull;

int main () {
#ifndef ONLINE_JUDGE
	ifstream fin("input.txt");
//	#undef cin
//	#define cin fin
#endif

	int a[] = {0, 1, 2, 3};
	int b[4];
	for(int i = 0; i < 4; i++)
		cin >> b[i];

	int mx = 0;
	do {
		mx = max(mx, b[a[0]] * b[a[1]] + b[a[2]] * b[a[3]]);
	}
	while(next_permutation(a, a+4));

	cout << mx;

	return 0;
}