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.util.Scanner;


public class A546 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub.
        Scanner scan = new Scanner(System.in);
        
        long k = scan.nextLong();
        long n = scan.nextLong();
        long w = scan.nextLong();
        
        long total = 0;
        for(int i = 1; i <= w; i++){
            total+=k*i;
        }
        long borrow = total - n;
        if(borrow<0){
            System.out.println(0);
        }else{
            System.out.println(borrow);
        }
    }

}
