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
"""
https://codeforces.com/problemset/problem/546/A
"""


def function():
    k, n, w = map(int, (input().split()))

    costs = 0

    for i in range(1, w+1):
        costs = costs + i * k

    borrow = costs - n
    if borrow < 0:
        borrow = 0
    print(borrow)


if __name__ == "__main__":
    function()

"""
Read Input and split it in 3 integers
- cost of first banana = k
- money of soldier = n
- bananas he wants = w

costs = w * k + w -1 * k + ... 1 * k

Output money he needs to borrow
"""
