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
#count = input()
#print count

s = raw_input()

s = s.split(" ")

k = int(s[0])
n = int(s[1])
w = int(s[2])

all_cost = 0

for i in xrange(1, w+1):
    all_cost += i*k
#   print i*k

#print all_cost
need = all_cost - n 

#print n , all_cost
#print k , all_cost
if (need == 0 or need < 0):
    print 0
else:
    print need

#print s
