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 retrieve_input():
    sab_list = [int(x) for x in raw_input().split()]
    return sab_list

def soldier_and_bananas(sab_list):
    k, n, w = sab_list[0], sab_list[1], sab_list[2]
    dollars = k *(w*(w+1)/2) - n
    if dollars <= 0:
        return 0
    return dollars

def main():
    sab_list = retrieve_input()
    #sab_list = [3, 17, 4]
    print soldier_and_bananas(sab_list)
    
if __name__ == '__main__':
    main()