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 sys import stdin, exit

# `num_bananas` in range [0, 10**9]
first_banana_cost_str, soldier_money_str, num_bananas_str = stdin.readline().strip().split(' ')
first_banana_cost, soldier_money, num_bananas = int(first_banana_cost_str), int(soldier_money_str), int(num_bananas_str)

if num_bananas == 0:
    print(0)
    exit(2)

total_bananas_cost = first_banana_cost
for i in range(2, num_bananas+1):
    total_bananas_cost += first_banana_cost * i

money_to_borrow = total_bananas_cost - soldier_money
output = money_to_borrow if money_to_borrow > 0 else 0
print(output)
