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.Arrays;
import java.util.Collections;
import java.util.Scanner;

public class Main {

    static int gcd(int a, int b) {


        while (a != b) {
            if (a > b)
                a = a - b;

            else

                b = b - a;
        }


        return a;
    }


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

        int k,n,w;

        k = in.nextInt();
        n = in.nextInt();
        w = in.nextInt();

        int totalAmm = k*(w*(w+1)/2);

        if (totalAmm <= n)
            System.out.println("0");
        else
            System.out.println(totalAmm - n);

    }
}