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
allstuff = input() + " "
l = []
current = ""
for i in range(len(allstuff)):
    if allstuff[i] != " ":
        current += allstuff[i]
        if i != len(allstuff) - 1 and allstuff[i+1] == " ":
            current = int(current)
            l += [current]
            current = ""
        
        
cost = l[0]
money = l[1]
bananas = l[2]
total = 0

for i in range(1, bananas+1):
    total += (cost*i)
    
if money>total:
    print(0)
else:
    print(total-money)