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
"""
https://codeforces.com/problemset/problem/546/A
"""
# k = cost of the first bananna
# n = initial no of dollars the soldier has
# w = no of bananas he want

if __name__ == "__main__":
    k, n, w = map(int, input().strip().split())
    total_cost = 0
    for i in range(1, (w+1)):
        total_cost += i*k
    if (total_cost - n) >= 0:
        print(total_cost - n)
    else:
        print("0")