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.util.*;
//import java.io.*;
//import java.math.*;
public class Lucky{
    public static void main(String args[]) /*throws IOException*/ {
        //BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        Scanner sc=new Scanner(System.in);
        long k=sc.nextLong(),n=sc.nextLong(),w=sc.nextLong(),total=0;
        for(long i=0;i<w;i++){
            total+=(i+1)*k;
        }
        if(total<=n)
            System.out.print("0");
        else System.out.print(total-n);
    }
}