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
from math import sqrt, floor

def loan_size(line):
    """
    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≤10^9), 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.
    """

    num_list = list(map(int, line.split(" ")))
    base_cost = num_list[0]
    starting_money = num_list[1]
    bananas_desired = num_list[2]

    # determine total cost of bananas
    total_cost_bananas = (bananas_desired*(bananas_desired+1)*base_cost)//2

    if total_cost_bananas <= starting_money:
        print(0)
    else:
        print(total_cost_bananas - starting_money)


if __name__ == "__main__":

    input_str = input()
    loan_size(input_str)
