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
A = input()
B = []
for i in A.split():
    B.append(int(i))
if ((B[0]+(B[2]*B[0]))*B[2])/2>B[1]:
    sum = ((B[0]+(B[2]*B[0]))*B[2])/2-B[1]
else:
    sum = 0
print(int(sum))