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
import sys
import os
# import math
# input = sys.stdin.readline

def int_array():
    return list(map(int, input().strip().split()))


def str_array():
    return input().strip().split()

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

def take_input():
	if os.environ.get("check"):
		sys.stdin = open('input.txt', 'r') 
		sys.stdout = open('output.txt', 'w')
		
take_input()
######################### TEMPLATE ENDS HERE #################################

c, k, b = int_array()
paisa = 0
count = 1
for i in range(b):
	paisa+=count*c
	count+=1

if k - paisa < 0:
	print(abs(k-paisa))
else:
	print(0)