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

def func(k, n, w):
    if w <= 0:
        return 0
    s = 0
    i = 1
    while i <= w:
        s += i*k
        i += 1
    if s <= n:
        return 0
    return s-n

if __name__ == '__main__':

    k, n, w = tuple(map(int, input().split()))
    print(func(k, n, w))
