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 math import pi, gcd, factorial
from collections import defaultdict, Counter
from heapq import heapify, heappop, heappush
from sys import maxsize
mod1 = 10**(-9)
mod1 = (10**9) + 7

########################### Input #############################
def input_t():
	return int(input())

def input_f():
	return float(input())

def input_list():
	return [int(num) for num in input().split()]

########################## Output #############################
def print_c(i, res):
	print("Case {}: {}".format(i+1, res))

def print_e(i, res):
	print("Case {} = {}".format(i+1, res))

########################## Tarminate #########################
def max_min():
	return (maxsize, -maxsize-1)

def tar(a, b, c):
	if a == b == c == 0:
		exit()
##############################################################

def solve():
	k, w, n = input_list()
	s = (n* n + n) // 2
	#print(s)
	print(max(0, k*s-w))

if __name__=="__main__":
	solve()