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

def mGetThePrice(k,w):
    Summation = 0
    for index in range(1,w+1):
        Summation += index * k
    return Summation

def main():
    try:
        InputArray = list(map(int,input().split()))
        if (InputArray.__len__().__eq__(0)): exit()
        k = InputArray[0]
        n = InputArray[1]
        w =  InputArray[2]
        if (
            InputArray.__len__().__eq__(3) and 0 <= n <= pow(10,9)  and
            k >= 1 and w <= 1000 
            ):
            price = mGetThePrice(k,w)
            debt = abs(n-price) if n<price else 0
            print(debt)

        else:
            exit(0)
    except ValueError as e:
        pass

if __name__ == "__main__":
    main()