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
from sys import stdin,stdout
from collections import Counter
from math import ceil
from bisect import bisect_left 
from bisect import bisect_right
import math
 
def ai(): return list(map(int, stdin.readline().split()))
def ei(): return map(int, stdin.readline().split())
def ip(): return  int(stdin.readline().strip())
def op(ans): return stdout.write(str(ans) + '\n')

k,n,w=ei()
s=0
for i in range(1,w+1):
    s+=k*i 
if s-n<0:
    print(0)
else:
    print(s-n)