#include <iostream>
#include <limits.h>
#include <cmath>
#include <string>
#include <stdio.h>
#include <algorithm>
#include <stdlib.h>
#include <vector>
#include <stack>
#include <map>

using namespace std;


int i,n,v[10],maxim=0;

int main()
{
    for(i=1; i<=4; i++)
        cin>>v[i];

    sort (v+1,v+4+1);

    do
    {
        maxim = max ( maxim , v[1]*v[2] + v[3]*v[4]);
    }
    while(next_permutation(v+1,v+4+1));
    cout<<maxim;

    return 0;
}