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 SoldierAndBananas {

    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 sum = (((w * (w + 1)) * k) / 2);
         if (sum - n < 0 ){
         
         System.out.println("0");
         }else{
             
             System.out.println(sum - n);
         } 
    }
    
}