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

s = input()
j = s.split()
for i in range(len(j)):
    if i == 0:
        k = int(j[0])
    elif i == 1:
        n = int(j[1])
    else:
        w = int(j[2])
if 1<=k and w<=1000 and 0<=n<=10**9:
    s = 0
    for i in range(1,w+1,1):
    
        j = i*k
        s = s + j
    s = s-n
    if s<=0:
        print(0)
    else:
        print(s)