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
import sys
##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.

line = sys.stdin.readline()

while line: 
    k,n,w  = line.split()
    k = int(k)
    n = int(n)
    w = int(w)
    ### do things append to solution
    ##  cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.
    ## k , n , w 

    tot = 0
    cost = k 
    for i in range(w):
        tot +=  (i+1) *cost 

    borrow = tot - n
    if borrow < 0:
        borrow = 0
    print(borrow)
        

        #2^1k + 2^2k +2^3 + 2^4k


    line = sys.stdin.readline()