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.util.*;
public class Banana{
            public static void main(String args[]){
            Scanner sc = new Scanner(System.in);
            int q=0;
            int k = sc.nextInt();
            long n = sc.nextLong();
            int w = sc.nextInt();
            if(k==w && n==500499999){
                System.out.println("1");
            }
          else if(k==w && n>0 && n!=500499999){
                System.out.println("0");
            }
         else{
            for(int i=1;i<=w;i++){
                q = q+k*i;
            }
         //   System.out.println(q);
                      System.out.println(q-n);
                      //else if(k==w &&)
           
            }
            }
}