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()
ii = 0
fprob = sprob = 0
for l in s:
    if l == ' ' and fprob == 0:
        fprob = ii
    elif l == ' ' and sprob == 0:
        sprob = ii
    ii += 1    
k = int(s[0:fprob])
n = int(s[fprob+1:sprob])
w = int(s[sprob+1:len(s)])
ii = 0
doll = 0
for i in range(1, w + 1):
    ii += 1
    if ii <= w:
        doll = doll + k * ii
if doll > n:
    print(doll - n)
else:
    print(0)
