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

public class prog {
	public static int spell(ArrayList<Integer> list) {
		Collections.sort(list);
		return list.get(3) * list.get(2) + list.get(1) * list.get(0);		
	}
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		ArrayList<Integer> list = new ArrayList<Integer>();
		for (int i = 0; i < 4; i++) {
			list.add(s.nextInt());
		}
		
		System.out.println(spell(list));
		
		s.close();		
	}
}