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
/*
author :- Shubham Saini
 

*/
import java.util.Collections;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Arrays;
import java.util.*;
import java.lang.*;
import java.io.*;

 
public class june
{   
	public static void main (String[] args) throws IOException
	{    
	   Scanner sc = new Scanner(System.in);
	   int k=sc.nextInt();
	   int n=sc.nextInt();
	   int w=sc.nextInt();
	   int sum=0;
	   
	   for(int i=1;i<=w;i++)
	   {
	       sum=sum+(i*k);
	   }
	   int total=sum-n;
	   if(total<0)
	   {
	       System.out.println("0");
	   }
	   else{
	   System.out.println(total);
	   }
	}
}