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 soldier
{
   public static void main(String args[])
   {
      Scanner s=new Scanner(System.in);
   int k=s.nextInt();
   int n=s.nextInt();
   int w=s.nextInt();
   int sum=0;
   for(int i=0;i<w;i++)
   {
      sum+=k*(i+1);
   }
   if(sum>n)System.out.println(sum-n);
   else System.out.println(0);
}
}