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

using namespace std;

int st[10];
int a[10];
int maxim = 0;

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

    for ( int i = 1; i <= 4; ++i )
            st[i] = i;

    do
    {
        maxim = max( maxim, a[ st[1] ] * a[ st[2] ] + a[ st[3] ] * a[ st[4] ] );

    } while ( next_permutation( st + 1, st + 4 + 1 ) );

    cout << maxim;

    return 0;
}