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.io.*;
import java.lang.Math.*;
import java.util.regex.*;

 public class soldier{
	public static void main(String[] args) {
		try{
			BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
			String input = read.readLine();
			String array[] = input.split(" ");
			double k = Double.parseDouble(array[0]);
			double w = Double.parseDouble(array[2]);
			double money_required = w*(w+1);
			double sss = money_required/2;
			double money_posses = Double.parseDouble(array[1]);
			double ans = (sss*k)- money_posses;
			if (ans<0.0) {
				ans=0.0;
			}
			System.out.println((int)ans);
		}
		catch(Exception e){

		}
	}
}