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

line = raw_input()
words = line.split()

cost_of_first_banana = int(words[0])
initial_dollars = int(words[1])
num_bananas_wanted = int(words[2])

total_cost_of_bananas = 0
for x in range(1, num_bananas_wanted + 1):
   total_cost_of_bananas = total_cost_of_bananas + (x*cost_of_first_banana)

have_to_borrow_dollars = total_cost_of_bananas - initial_dollars
if (have_to_borrow_dollars < 0):
   have_to_borrow_dollars = 0

print(have_to_borrow_dollars)
