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 math import *
from collections import deque
from copy import deepcopy
import sys
def inp(): return sys.stdin.readline().rstrip("\r\n") #for fast input
def multi(): return map(int,input().split())
def lis(): return list(map(int, inp().split()))
def out(var): sys.stdout.write(str(var))  #for fast output, always take string
def printlist(a) :
    for p in range(0,len(a)):
        out(str(a[p]) + ' ')

def isPrime(n) :
    if (n <= 1) : return False
    if (n <= 3) : return True
    if (n % 2 == 0 or n % 3 == 0) : return False
    i = 5
    while(i * i <= n) :
        if (n % i == 0 or n % (i + 2) == 0) :
            return False
        i = i + 6
    return True

#copied functions end

#start coding

k,n,w=multi()
if(((w+1)*k*(w/2)-n)<=0):
    print(0)
else:
    print(ceil(((w+1)*k*(w/2)-n)))

