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) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        String[] input = s.split(" ");
        int k = Integer.valueOf(input[0]);
        int n = Integer.valueOf(input[1]);
        int w = Integer.valueOf(input[2]);
        int sum = w*(w+1)/2;
        sum = sum*k;
        if(sum>n) {
        	System.out.println(sum-n);
        }else {
        	System.out.println(0);
        }
	}
}