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.*;

public class A {

    static BufferedReader in;
    static PrintWriter out;
    static StringTokenizer tok;

    public static void main(String[] args) throws IOException {
        try {
            in = new BufferedReader(new FileReader("sum0.in"));
            out = new PrintWriter(new File("sum0.out"));
        } catch (Exception e) {
            in = new BufferedReader(new InputStreamReader(System.in));
            out = new PrintWriter(new OutputStreamWriter(System.out));
        }

        tok = new StringTokenizer("");
        new A().solve();
        out.flush();
        out.close();
    }

    String nextTok() throws IOException {
        if (!tok.hasMoreTokens()) {
            tok = new StringTokenizer(in.readLine());
        }
        return tok.nextToken();
    }

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

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

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

    static class Pair implements Comparable<Pair> {

        long a;
        long b;

        public Pair( long a, long b) {

            this.a = a;
            this.b = b;
        }

        @Override
        public int compareTo(Pair o) {
            if (o.a < a) return 1;
            if (o.a > a) return -1;
            if (o.b > b) return -1;
            if (o.b < b) return 1;
            return 0;
        }
    }


    void solve() throws IOException {
        long k = nextLong();
        long n = nextLong();
        long w = nextLong();
        long res = 0;
        for (int i = 1; i <= w; i++) {
            res += i*k;
        }
        if (res - n < 0) System.out.println(0); else
        System.out.println(res - n);
    }

}
