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 Cf546a {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        // k dollars for the first banana
        // n dollars total before borrowing
        // w number of bananas to buy
        int k = input.nextInt();
        int n = input.nextInt();
        int w = input.nextInt();

        long totalCost = 0;
        for (int i = 0; i < w; i++) {
            totalCost += (i+1L)*k;
        }

        long borrow = Math.max(totalCost - n, 0);
        System.out.println(borrow);
    }
}
