#include <iostream>
using namespace std;

int f(int a,int b,int c,int d){
    return a*b + c*d;
}

int main(){

    int Ret = 0;
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    Ret = max(f(a,b,c,d),f(a,c,b,d));
    Ret = max(Ret,f(a,d,b,c));
    cout << Ret;
}