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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# cara pake rumus
# nb // divide ke floor = 8.5 => 8
# k,n,w=map(int,input().split()) #untuk input
# print(max(0, w * k * (1 + w) // 2 - n)) # ambil max

# cara GOBLOK
k,n,w=map(int,input().split())
total = 0
for i in range(1, w + 1):
    total += k * i
if total > n:
    print(total-n)
else :
    print(0)