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
# -*- coding: utf-8 -*-
"""
Created on Sat Oct  3 14:35:53 2020

@author: 章斯岚
"""
n=input().split()
k1=n[0];k2=n[1];k3=n[2]
k=int(k1);n=int(k2);w=int(k3)
money=k*(1+w)*w/2
if money>n:
    print(int(money-n))
else:
    print(0)