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
#  URL: http://codeforces.com/contest/546/problem/A
#  PROBLEM RESTATEMENT
#      Consider the sum s = k + 2k + 3k + ... wk (given k, w, and int n).
#      What is s - n?
#  APPROACH
#      (1) Factor out k => k * (1 + 2 + 3 + ... + w)
#      (2) The sum of an arithmetic series from 1 to n is n * (n + 1) / 2
#      (3) Compute k * w * (w + 1) / 2 - n.


def solve(k: int, n: int, w: int) -> int:
    cost = int(k * w * (w + 1) / 2)
    if cost - n > 0:
        return cost - n
    return 0


k, n, w = list(map(int, input().split()))
print(solve(k, n, w))
