import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;


public class prog {
    public static void main (String[] args) throws java.lang.Exception
    {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        String[] splitted = str.split(" ");
        List<Integer> numbers = new ArrayList<Integer>();
        numbers.add(Integer.parseInt(splitted[0]));
        numbers.add(Integer.parseInt(splitted[1]));
        numbers.add(Integer.parseInt(splitted[2]));
        numbers.add(Integer.parseInt(splitted[3]));
        Collections.sort(numbers);
        System.out.println(numbers.get(0)*numbers.get(1)+numbers.get(2)*numbers.get(3));
        scanner.close();
    }
}