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 Soldier_and_Bananas {
    public static void main(String[] args) {

        Scanner skaner = new Scanner(System.in);
        int k = skaner.nextInt(), n = skaner.nextInt(), w = skaner.nextInt();

        int suma = 0;

        for (int i = 0; i < w+1 ; i++) {
            suma = suma + (i*k);
        }
        if (n - suma <0 ) System.out.println(suma -n);
        else System.out.println(0);

    }
}
