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
while True:
    try:
        i = raw_input().split()
        k = int(i[0])
        n = int(i[1])
        w = int(i[2])
        need = 0
        c = 1
        total = 0
        for h in range(w):
            total += (c * k)
            c +=1
        if total > n :
            print total-n
        else:
            print 0

    except EOFError:
        break
