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
#!/usr/bin/python
import sys

n = 0
for l in sys.stdin:
    for k in l.split():
        if n == 0:
            ek = int(k)
        elif n == 1:
            en = int(k)
        elif n == 2:
            ew = int(k)
        n = n + 1
    break

finish = 0
cost = 0
loop = 1
while ew > 0:
    cost = cost + (ek * loop)
    ew = ew - 1
    loop = loop + 1

if cost > en:
    finish = cost - en

print(finish)
