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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;

public class Main {
	static BufferedReader in;
	static PrintWriter out;

	public static void main(String[] args) throws IOException {
		in = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(System.out);

		String[] tok = rst();
		long k = Long.parseLong(tok[0]);
		long n = Long.parseLong(tok[1]);
		long w = Long.parseLong(tok[2]);
		
		long cost = 0;
		for (int i=1;i<=w;i++) {
			cost+= (i*k);
		}
		
		long b = (n>=cost) ? 0 : (cost-n);
		out.println(b);
		
		in.close();
		out.close();
	}

	public static int ri() throws IOException {
		return Integer.parseInt(in.readLine());
	}

	public static long rl() throws IOException {
		return Long.parseLong(in.readLine());
	}

	public static String rs() throws IOException {
		return in.readLine();
	}

	public static String[] rst() throws IOException {
		return in.readLine().split(" ");
	}

	public static int[] rit() throws IOException {
		String[] tok = in.readLine().split(" ");
		int[] res = new int[tok.length];
		for (int i = 0; i < tok.length; i++) {
			res[i] = Integer.parseInt(tok[i]);
		}
		return res;
	}

	public static long[] rlt() throws IOException {
		String[] tok = in.readLine().split(" ");
		long[] res = new long[tok.length];
		for (int i = 0; i < tok.length; i++) {
			res[i] = Long.parseLong(tok[i]);
		}
		return res;
	}


}
