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.ArrayList;
import java.util.Arrays;
import java.lang.*;
import java.util.Scanner;

/**
 * Created by Preeti Kanaujiya on 10/9/2016.
 */
public class codeforces {

    public static void main(String args[]) {

        Scanner input = new Scanner(System.in);
     int k= input.nextInt();
        int n = input.nextInt();
        int w = input.nextInt();
        int ans = (int)(k*w*(w+1)/2);
        int r = 0;
        if(ans>n)
        {
            r = ans - n;
        }
        System.out.print(r);

    }
}
