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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * Created by surya on 19-Mar-17.
 */
public class SoldierAndBananas {
    public static void main(String[] args)throws IOException
    {
        BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
        int k,n,w;
        String[] str=br.readLine().split(" ");
        k=Integer.parseInt(str[0]);
        n=Integer.parseInt(str[1]);
        w=Integer.parseInt(str[2]);
        int ans=(k*w*(w+1))/2-n;
        if(ans<=0)
            System.out.println("0");
        else
            System.out.println(ans);

    }
}
