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 ceil
import sys,bisect,copyreg,copy,statistics,os
def inp(): return sys.stdin.readline().strip()
def IIX(): return (int(x) for x in sys.stdin.readline().split())
def II(): return (int(inp()))
def LI(): return list(map(int, inp().split()))
def L(x):return list(x)
def out(var): return sys.stdout.write(str(var))


k, n, w=IIX()

cost=k*((w*(w+1)//2))

if cost-n>=0:
    out(cost-n)
else:
    out(0)










