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.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.Stack;
import java.util.TreeSet;

public class Codeforces {
    //help func
    static boolean prime(long a)
    {
        for(int i=2;i*i<=a;i++)
        {
            if(a%i==0)
                return false;
        }
        return true;
        
        
    }
  /////////////////////////////
  public static void main(String[] args) {
  InputStreamReader is=new  InputStreamReader(System.in);
  BufferedReader br=new BufferedReader(is);
  ArrayList A=new ArrayList();
  TreeSet T=new TreeSet();
  Stack S=new Stack();
  Scanner read=new Scanner(System.in); 
  Map<String ,Integer>map=new HashMap<>();
  StringBuilder str= new StringBuilder();//don't any thing at specific index 
  ////////////////////////////////
  int a=read.nextInt();
  int b=read.nextInt();
  int c=read.nextInt();
  int res=0;
  for(int i=1;i<=c;i++)
  {
      res+=i*a;
  }
  if(res>b)
          System.out.println(Math.abs(b-res));
  else
          System.out.println(0);
  }
  
}
 