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 f(lst):
    '''
    >>> f([3, 17, 4])
    13
    '''
    price = lst[0]
    money = lst[1]
    amount = lst[2]
    total = 0

    for i in range(int(amount + 1)):
        s = price * i
        total = total + s


    if total - money < 0:
        return 0
        
    return total - money


print(f(list(map(int, input().split()))))