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
//NAVI WILL WIN ESL PRO LEAGUE
//ASH
import java.util.Scanner;
public class sum1 {

	public static void main(String[] args) {
		
		Scanner ad=new Scanner(System.in);
		int k=ad.nextInt();//banana cost
		int n=ad.nextInt();//DOLLARS
		int w=ad.nextInt();//no of bananas
		
		
		int ans=(k*w*(w+1))/2-n;
		
		if (ans<0) 
			ans=0;
			System.out.println(ans);
					
	
		}
}
