#include <string>       // std::string
#include <iostream>     // std::cout
#include <sstream> 

using namespace std;

int main()
{

int a;
int b;
int c;
int d;

    string tmp;
    getline(cin, tmp);
    stringstream ss(tmp);
    ss >> a; ss >> b; ss >> c; ss >> d;
    
    int max = -1;
    int sum1 = a*b + c*d;
    if (sum1 > max) max=sum1;
    int sum2 = a*c + b*d;
    if (sum2 > max) max=sum2;
    int sum3 = a*d + c*b;
    if (sum3 > max) max=sum3;

    cout<<max;

    return 0;
}