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

Solution: Using the AP formula, the total money needed is (1+2+..w)*k
That simplifies to ((w*(w+1)) * k)/2. This is the sum of first w natural numbers, multiplied by k
Then take the difference of that with soldier's initial money, which is n. If he does not need money, we need to set 0.
Hence we use max to compare the the difference against 0.
'''

def solve(k, n, w):

    totalMoneyNeeded = ((w*(w+1)) * k)/2
    return max(totalMoneyNeeded - n, 0)


if __name__ == "__main__":
    inputs = raw_input().split(" ")
    print solve(int(inputs[0]), int(inputs[1]), int(inputs[2]))