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 = map( int, raw_input().split( " " ) )

k = x[0]
n = x[1]
w = x[2]

i = 1
tot_ban = 0
bor = 0

while n >= k*i:
    n -= k*i
    tot_ban += 1
    i += 1
    
while i <= w:
    bor += k*i
    i += 1

if bor == 0:
    print "0"
else:
    print "%d" % ( bor-n )