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
w = 0
k = 0
n = 0
a = input()
chs = ''
dv = False
nm = 0
for i in a:
    if i != ' ':
        chs += i
    else:
        if dv == False:
            k = int(chs)
            dv = True
        else:
            n = int(chs)
        chs = ''
w = int(chs)
i = 1
for a in range(w):
    nm += int(k) * int(i)
    i += 1
if nm <= n:
    print('0')
else:
    print(nm - n)



