#include <iostream>
#include <fstream>
using namespace std;

ifstream f("date.in");

int a[4];

int main()
{
    cin >> a[0] >> a[1] >> a[2] >> a[3] >> a[4];

    int mx = 0;
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4; j++) {
            if (i == j) {
                continue;
            }
            for (int k = 0; k < 4; k++) {
                if (k == i || k == j) {
                    continue;
                }
                for (int l = 0; l < 4; l++) {
                    if (l == i || l == j || l == k) {
                        continue;
                    }
                    mx = max(mx, a[i] * a[j] + a[k] * a[l]);
                }
            }
        }
    }
    cout << mx << endl;

    return 0;
}