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;

public class soldier_and_banas {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String str = br.readLine();
        String s[] = str.split(" ");
        int kk = Integer.parseInt(s[0]);
        int r= Integer.parseInt(s[1]);
        int w = Integer.parseInt(s[2]);
        //System.out.println(((k * w) - n) 0 ? 0: );
       int bal=(((w*(w+1))/2)*kk);
        System.out.println(bal>r?bal-r:0);
    }

}
