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 Main
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int k = input.nextInt() , n = input.nextInt() , w = input.nextInt() , sum = 0 , i = 0;
        while (w>0)
        {
            sum+=((i+1)*k);
            w--;
            i++;
        }
        if (n>=sum)
            System.out.print(0);
        else
            System.out.print(sum-n);
    }
}