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 Fun {
	public static void main(String[]args){
		Scanner s = new Scanner(System.in);
		int k=s.nextInt();
		int n=s.nextInt();
		int w=s.nextInt();
		int total=0;
		for(int i=1;i<=w;i++){
			total+=i;
		}
		if(total*k-n<1) System.out.println("0");
		else System.out.println(total*k-n);
	}
}
