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 Main {
    public static void main(String[] args) throws NumberFormatException,
            IOException {

        BufferedReader br = new BufferedReader(
                new InputStreamReader(System.in), 1024 * 1024 * 2);

        int[]v = readArrayLine(br.readLine(),3);
        int k = v[0];
        int n = v[1];
        int w = v[2];

        System.out.println(Math.max(0, k * w * (w+1) / 2 - n));
    }

    public static int[] readArrayLine(String line, int n) {
        int[] ret = new int[n];
        int start = 0;
        int end = line.indexOf(' ', start);
        for (int i = 0; i < n; i++) {
            if (end > 0)
                ret[i] = Integer.parseInt(line.substring(start, end));
            else
                ret[i] = Integer.parseInt(line.substring(start));
            start = end + 1;
            end = line.indexOf(' ', start);
        }
        return ret;
    }
}
