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;
import java.util.*;
 
public class solution{
    
    public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    
    int k = sc.nextInt();
    int n = sc.nextInt();
    int w = sc.nextInt();
    int sum, res;
    
    sum = (int)((w*(w+1))/2)*k;
    res = (int)(sum - n);
    
    if(res<0)
    {
        System.out.print(0);
    }
    else{
        System.out.print(res);
    }
 
}
}