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.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {
  
  
  
 public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        int k,n,w,answer,price;
        k=in.nextInt();
        n=in.nextInt();
        w=in.nextInt();
        price=(k*w*(w+1))/2;
        if(n>=price)answer=0;
        else answer=price-n;
        
        System.out.println(answer);
        
   }
}