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
a_complex_list = input()
a_complex_list = a_complex_list.split(" ")
price_for_a_banana = int(a_complex_list[0])
pocket = int(a_complex_list[1])
number_of_bananas = int(a_complex_list[2])
sum = 0
if number_of_bananas != 0:
    for c in range(1, number_of_bananas + 1, 1):
        #print(sum)
        sum = sum + price_for_a_banana * c
if pocket <= sum:
    amount_to_borrow = sum - pocket
elif pocket > sum:
    amount_to_borrow = 0
print(amount_to_borrow)