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
import sys

class Scanner:

    def __init__(self):
        self.current_tokens = []

    def remaining_tokens(self):
        return len(self.current_tokens)

    def nextline(self):
        assert self.remaining_tokens() == 0, "Reading next line with remaining tokens"
        return input()

    def nexttokens(self):
        return self.nextline().split()
    
    def nexttoken(self):
        if len(self.current_tokens) == 0:
            self.current_tokens = self.nexttokens()
        assert self.remaining_tokens() > 0, "Not enough tokens to parse."
        return self.current_tokens.pop(0)

    def nextints(self, n=-1):
        if n == -1:
            return list(map(int, self.nexttokens()))
        else:
            return (self.nextint() for i in range(n))
    
    def nextint(self):
        return int(self.nexttoken())

def quit():
    sys.exit(0)

stdin = Scanner()
nextint = stdin.nextint
nextints = stdin.nextints
nextline = stdin.nextline

k,n,w = nextints(3)

c = 0
for i in range(w):
    c += (i + 1) * k

print(max(0, c-n))
