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.math.BigInteger;
import java.util.Scanner;

public class Soldier_and_bananas {

	public static void main(String[] args) {
		
		int k,w;
		BigInteger total = BigInteger.ZERO;
		BigInteger n;
		
		Scanner reader = new Scanner(System.in);
		
		k = reader.nextInt();
		n = reader.nextBigInteger();
		w = reader.nextInt();
		
		for(int i=0;i<w;i++)
		{
			total = total.add(BigInteger.valueOf((i+1)*k));
		}
		
		if(n.subtract(total).compareTo(BigInteger.ZERO) <= 0)
		{
			System.out.println(total.subtract(n));
		}
		else
			System.out.println(0);

	}

}
