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
#-*-coding:utf-8-*-

import string
import sys
reload(sys)
sys.setdefaultencoding('utf-8')

# w개의 바나나를 구매
# 첫 바나나 k 달러, 다음 바나나 2*k달러.....(i*k달러)
# n달러를 가지고 있음
# 얼마를 더 빌려야 w개의 바나나를 구매할 수 있는가?


num = raw_input()

# n[0] = k    n[1] = n    n[2] = w 
n = num.split()

# 바나나의 총가격을 구한뒤, 원래 가지고 있는 액수를 뺌
sum = 0
for i in range(int(n[2])) :
	sum = sum + int(n[0])*(i+1)

if sum-int(n[1]) >=0 : print sum-int(n[1])
else 				 : print '0'
