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
#problem/546/A
# input
# cost_of_1st_banana initial_dollars(x) number_of_bananas
# cost_of_i^th_banana = k
# number_of_bananas = w
# o/p amt. of dollars to borrows -> y
# k + 2k + ... + i*k = (i(i+1)/2)*k
# x + y = 
k,x,w = map(int,input().split())
z = int(k*((w**2+w)/2)-x)
if z>0:
    print(z)
else:
    print(0)
