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





#3 17 4

#3 1 3 = 3 -> 17 - 3 = 14
#3 2 6 = 3 + 6 -> 14 - 6 = 8
#3 3 9 = 3 + 6 + 9 -> 8 - 9 = -1
#3 4 12 = 3 + 6 + 9 + 18 -> -1 + 12 = -13

cb_sd_bw = list(map(int, input().split()))
cost_banana = cb_sd_bw[0]
soldier_dollars = cb_sd_bw[1]
quantity = cb_sd_bw[-1]
total_cost = 0

for i in range(1,quantity+1):
    total_cost += i * cost_banana


if total_cost - soldier_dollars <= 0:
    print('0')
else:
    print(total_cost - soldier_dollars)
