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 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
"""

total = 0

banana_cost, money, banana_count = input().split()
banana_cost = int(banana_cost)
banana_count = int(banana_count)
money = int(money)

for i in range(1, banana_count+1):
    total += (i * banana_cost)

print((total-money) if total>money else '0')
