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 com.company;
import java.io.*;
import java.util.*;
import java.math.*;

public class Solution implements Runnable {
    static String filename = "";
    static boolean fromFile = false;
    BufferedReader in;
    PrintWriter out;
    FastScanner sc;

    public static void main(String[] args) {
        new Thread(null, new Solution(), "", 1 << 25).start();
    }

    public void solve() throws Exception {
        int k = sc.nextInt();
        int n = sc.nextInt();
        int w = sc.nextInt();
        int res = (k*(1+w)*w)/2-n;
        if (res < 0) {
            res = 0;
        }
        System.out.println(res);
    }

    public void run() {
        try {
            init();
            solve();
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            out.close();
        }
    }

    void init() throws Exception {
        if (fromFile) {
            in = new BufferedReader(new FileReader(filename+".in"));
            out = new PrintWriter(new FileWriter(filename+".out"));
        } else {
            in = new BufferedReader(new InputStreamReader(System.in));
            out = new PrintWriter(System.out);
        }
        sc = new FastScanner(in);
    }
}

class FastScanner {

    BufferedReader reader;
    StringTokenizer strTok;

    public FastScanner(BufferedReader reader) {
        this.reader = reader;
    }

    public String nextToken() throws IOException {
        while (strTok == null || !strTok.hasMoreTokens()) {
            strTok = new StringTokenizer(reader.readLine());
        }

        return strTok.nextToken();
    }

    public int nextInt() throws IOException {
        return Integer.parseInt(nextToken());
    }

    public long nextLong() throws IOException {
        return Long.parseLong(nextToken());
    }

    public double nextDouble() throws IOException {
        return Double.parseDouble(nextToken());
    }

    public BigInteger nextBigInteger() throws IOException {
        return new BigInteger(nextToken());
    }

    public BigDecimal nextBigDecimal() throws IOException {
        return new BigDecimal(nextToken());
    }
}
