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

def main():

    # Read input
    i = input().split()
    k = int( i[0] ) # Cost of 1st banana
    n = int( i[1] ) # Initial money
    w = int( i[2] ) # Number of bananas he wants

    s = (w*(w+1))/2 # sum of numbers from 1 to w
    t = int(s*k) # total cost
    b = t-n # amount to borrow

    if b>0:
        print(t-n)
    else:
        print(0)

if __name__ == '__main__':
    main()