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
#tt = int(input())

#while tt:
    #tt -= 1
    #k = int(input())
l = list(map(int,input().split()))

a = l[0]
b = l[1]
c = l[2]
n = 0
ll = []
for i in range(c):
    n += 1
    ll.append(n)
aa = []
for i in ll:
    i = i*a
    aa.append(i)
ss = sum(aa)

if ss <= b:
    print('0')
else:
    print(ss-b)