import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        int y = sc.nextInt();
        int k = sc.nextInt();
        if(x >= y){
            System.out.println(x);
        }else {
            if(x + k >= y){
                System.out.println(y);
            }else {
                int d = x + k;
                System.out.println(d + (y - d) * 2);
            }
        }
    }
}