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
from collections import deque, Counter, OrderedDict
from heapq import nsmallest, nlargest
def binNumber(n,size):
    return bin(n)[2:].zfill(size)

def gcd(a,b):
    if a == 0:
        return b
    return gcd(b%a,a)

#  =========     /\       /|    |====/|
#      |        /  \       |    |   / |
#      |       /____\      |    |  /  |
#      |      /      \     |    | /   |
#  ========= /        \  =====  |/====|  
#  code
if __name__ == "__main__":
    k,n,w = map(int,input().split())
    print(max(((w*(w+1))//2)*k - n,0))

    







