#include <iostream>  
#include <cmath>  
  
using namespace std;  
  
int main() {  
    int x, y, k;  
    cin >> x >> y >> k;  
  
    if (x > 0 && y > 0) {  
        if (x >= y) {  
            cout << x << endl;  
        } else if (x + k >= y) {  
            cout << y << endl;  
        } else {  
            cout << 2 * y - x - k << endl;  
        }  
    } else if (x < 0 && y < 0) {  
        if (x <= y) {  
            cout << -x << endl;  
        } else if (x - k <= y) {  
            cout << -y << endl;  
        } else {  
            cout << x - k - 2 * y << endl;  
        }  
    } else {  
        cout << min(2 * abs(y) + abs(x), abs(x) + abs(y) <= k ? 2 * abs(x) + abs(y) : 3 * abs(x) + 2 * abs(y) - k) << endl;  
    }  
    return 0;  
}

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);
            }
        }
    }
}