human
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
k, n,
=====
Write me a the Python code you requested?
assistant
#Here is the Python code you requested.
 w = map(int, raw_input().split())

def solve(k, n, w):
    def costo(w, k):
        return k * w * (w + 1) / 2
    if costo(w, k) <= n:
        return 0
    return costo(w, k) - n

print solve(k,n,w)