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
# A. Soldier and Bananas
# time limit per test
# 1 second
# memory limit per test
# 256 megabytes
# input
# standard input
# output
# standard output

# 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



if __name__ == '__main__':
    line = input().split(' ')
    dollars_per_banana = int(line[0])
    has_dollars = int(line[1])
    num_bananas = int(line[2])
    total = [x for x in range(dollars_per_banana * num_bananas, 0, -dollars_per_banana)]
    owe = sum(total) - has_dollars
    if owe < 0:
        print(0)
    else:
        print(owe)
