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. Soldier and Bananas
time limit per test1 second
memory limit per test256 megabytes
inputstandard input
outputstandard output
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
inputCopy
3 17 4
outputCopy
13
'''
INPUT_VALUE = str(input()).split(' ')
ALL_DOLLARS = 0
FIRST_DOLLARS = int(INPUT_VALUE[0])
for i in range(0,int(INPUT_VALUE[2])):
    ALL_DOLLARS += FIRST_DOLLARS*(i+1)
BORROW_DOLLARS = int(INPUT_VALUE[1]) - ALL_DOLLARS
if BORROW_DOLLARS < 0:
    print(abs(BORROW_DOLLARS))
else:
    print(0)