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
#-------------------------------------------------------------------------------
# Name:        module3
# Purpose:
#
# Author:      lihua
#
# Created:     27/08/2017
# Copyright:   (c) lihua 2017
# Licence:     <your licence>
#-------------------------------------------------------------------------------

k,n,w=map(int, raw_input().split())
cost=(k*w*(w+1))/2
if cost > n:
    print cost-n
else:
    print 0

