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
# Tasks
# - Create a script to `WORDLIST` problem using the .in and .out files
# - IMPLEMENT ROT13, ROT47, ETC...
# - Implement combinations(arr, r) -> returns all possible combinations or a generator
# --------------------
# 158 B - Taxi
# n = int(input())
# A = list(map(int, input().split()))
# A.sort(reverse=True)
# count = 0
# # write your greedy code here...
# print(count)
# --------------------
k, n, w = map(int, input().split())
cost_of_bananas = (k * w * (w + 1)) // 2
# print(cost_of_bananas)
if n > cost_of_bananas:
    print('0')
else:
    print(cost_of_bananas - n)
