import java.util.Scanner;

public class prog {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		int[] a = new int[4];
		a[0] = input.nextInt();
		a[1] = input.nextInt();
		a[2] = input.nextInt();
		a[3] = input.nextInt();
		
		int temp = 0;
		for (int i = 0; i < 3; i++){
			if (a[i] < a[i+1]){
				temp = a[i];
				a[i] = a[i+1];
				a[i+1] = temp;
			}
		}
				
		System.out.println(a[0]*a[1]+a[2]*a[3]);
	}
}