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.IOException;
import java.io.InputStreamReader;
import java.io.BufferedReader;
public class Main{
	 public static void main(String[]args)throws IOException,NumberFormatException{
		 BufferedReader bf=new BufferedReader(new InputStreamReader(System.in));
		 String s=bf.readLine();
		 String[]sa=s.split(" ");
		 int k=Integer.parseInt(sa[0]);
		 int n=Integer.parseInt(sa[1]);
		 int w=Integer.parseInt(sa[2]);
		 int c=0;
		 for(int i=1;i<=w;i++){
			 c+=i*k;
		 }
		 System.out.println((c-n)>0? c-n : 0 );
	 }
}