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
/* package codechef; // don't place package name! */

import javax.crypto.spec.PSource;
import java.security.AlgorithmConstraints;
import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
public class Cocechef {
    public static void main(String[] args) throws java.lang.Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String s[]= br.readLine().split(" ");
        int k=Integer.parseInt(s[0]);
        int n=Integer.parseInt(s[1]);
        int w=Integer.parseInt(s[2]);
        int sum=0;
        for(int i=1;i<=w;i++)
            sum+=k*i;
        System.out.println(sum<=n?"0":(sum-n));
    }
}









