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.*;

public class sab {
    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

 public static void main(String[] args) throws IOException {
 String[] split = br.readLine().split(" ");
        
        int k = Integer.parseInt(split[0]); 
        int n = Integer.parseInt(split[1]); 
        int w = Integer.parseInt(split[2]); 
        
         int total = w*(w+1)/2 * k;
           if(n >= total) pw.println(0);
        else pw.println(total - n);
        
        pw.close();
}
}
