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.math.*;
	//import java.text.DecimalFormat;
	import java.util.*;
	public class Temp2 {
		  public static void main(String[] args)
		  {
			Scanner sc = new Scanner(System.in);
			long k=sc.nextLong();
			long n=sc.nextLong();
			long w=sc.nextLong();
			int price=0;
			for(int i =1;i<=w;i++)
				price+=i*k;
			if(price>=n)
				System.out.println(price-n);
				else
					System.out.println(0);
		  }
	}

