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.util.*;
public class cat {
public static void main(String[] args)
{
	Scanner in=new Scanner(System.in);
	 long k,n,w;
	k=in.nextInt(); // стоимость первого банана
	n=in.nextInt(); // число денег
	w=in.nextInt(); // сколько хочет купить
	long cena;
	cena=w*(w+1)*k/2;
	if (cena<=n) System.out.print(0);
	else System.out.print(cena-n);
}
}