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
'''                      
   	
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I am a beginner. Feel free to send tutorials/help to srinivasan1995@gmail.com.

Codeforces, SPOJ handle: desikachariar.
Hackerrank, Codechef handle: Prof_Calculus.

Advices/Help are welcome. You will definitely get a thanks in return. Comments to be avoided.

College: International Institute of Information Technology, Bangalore.

'''

import math

def fn():
	return

if __name__ == '__main__':
	k,n,w = [int(pp) for pp in raw_input().split(' ')]
	print max(k*(w*(w+1)/2) - n, 0)
