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
def hazineh(gh,te):
    hazine = 0
    zarib = 1
    while(te>0):
        hazine =  hazine + (zarib*gh)
        zarib = 1 + zarib
        te = te - 1
    return (hazine)
########################################
i = input().split(" ")
h = hazineh(int(i[0]),int(i[2]))
if h < int(i[1]) :
       print (0)
else: print (h - int(i[1]))