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
x = input()
c = 0
cost = ''
money = ''
num = ''
sum = 0
while ord(x[c]) != 32:
    cost = cost + x[c]
    c += 1
c += 1
while ord(x[c]) != 32:
    money = money + x[c]
    c += 1
c += 1
while ord(x[c]) != 32:
    num = num + x[c]
    c += 1
    if c == len(x):
        break
n = int(num)
k = int(cost)
l = int(money)
while n != 0:
    sum = sum + (k * n)
    n = n - 1
if l >= sum:
    print(0)
else:
    print(sum - l)