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
'''input
3 17 4
'''
from collections import defaultdict as dd
from collections import Counter as ccd
from itertools import  permutations as pp
from itertools import combinations as cc
from random import randint as rd
from bisect import bisect_left as bl
from bisect import bisect_right as br
import heapq as hq
import math 
'''
Author : dhanyaabhirami
Hardwork beats talent if talent doesn't work hard
'''
'''
Stuck?
See github resources
Derive Formula
Kmcode blog
CP Algorithms Emaxx
'''
mod=pow(10,9) +7
def inp(flag=0):
    if flag==0:
        return list(map(int,input().strip().split(' ')))
    else:
        return int(input())

# Code credits
# assert(debug()==true)
# for _ in range(int(input())):

k,n,w=inp()
print(max(0,-n+(k*w*(w+1))//2))