A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k dollars for the second one and so on (in other words, he has to pay i·k dollars for the i-th banana). 

He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?

Input

The first line contains three positive integers k, n, w (1 ≤ k, w ≤ 1000, 0 ≤ n ≤ 109), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants. 

Output

Output one integer — the amount of dollars that the soldier must borrow from his friend. If he doesn't have to borrow money, output 0.

Examples

Input

3 17 4


Output

13
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Created by d.mishchanka on 24/06/2016.
 */
public class Task546A {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);

        long k = scan.nextLong(), n = scan.nextLong(), w = scan.nextLong();

        pw.println(Math.max(k * w * (w + 1) / 2 - n, 0));

        pw.close();
        scan.close();
    }

}
