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
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Tue Oct 13 17:31:03 2020

@author: zuoxichen
"""
def String_to_Lists(String):
    list1=list(String.split(' '))
    return list1
def main_approach (list):
    k=int(list[0])
    n=int(list[1])
    w=int(list[2])
    i=0
    sums=0
    while i<w:
        i+=1
        a=i*k
        sums=sums+a
    if (sums-n)<0:
        print('0')
    else:
        print(sums-n)
str1=input()
list1=String_to_Lists(str1)
main_approach(list1)