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
#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import time
import sys
import io
import re
import math
import itertools
#sys.stdin=file('input.txt')
#sys.stdout=file('output.txt','w')
#10**9+7
mod=1000000007
#mod=1777777777
pi=3.141592653589
xy=[(1,0),(-1,0),(0,1),(0,-1)]
bs=[(-1,-1),(-1,1),(1,1),(1,-1)]
#start = time.clock()
k,n,w=map(int,raw_input().split())
ans=chk=0
for i in range(1,w+1):
    ans+=i*k
print ans-n if ans>n else 0
#end = time.clock()
#print end - start