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.Scanner;

public class SoldierAndBananas_546A {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        //cost of first banana
        int k = sc.nextInt();
        //Initial number of $ soldier has
        int n = sc.nextInt();
        //number of bananas he wants
        int w = sc.nextInt();

        //k dollars for the first banana
        //2k dollars for the second banana
        //ik dollars for the i-th banana
        //how many dollars he has to borrow to buy w bananas
        //4 bananas, 3 - 1 banana = 3 + 3*2 + 3*3 + 3*4
        int amount = 0;
        for (int i = 1; i <= w; i++) {
            amount += k * i;
        }
        System.out.println((amount - n < 0) ? 0 : amount - n);
    }

}