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
# your code goes here
 
import sys
 
if __name__ == '__main__':
    wtf = sys.stdin.read()
    wtf = wtf.split('\n')[0]
    wtfs = wtf.split(' ')
    
    a1 = int(wtfs[0])
    
    d = a1
    s = int(wtfs[1])
    n = int(wtfs[2])
    an = a1 + (n - 1) * d
    sum = int(n * (a1 + an) / 2)
    ans = 0
    if sum > s:
    	ans = sum - s
    print(ans)