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
import sys
import io
import os

total = 0
failed = 0
def run(test,res):
    x = io.StringIO()
    with io.StringIO(test) as sys.stdin:
        with x as sys.stdout:
            work()
            z = x.getvalue().strip()
    sys.stdout = sys.__stdout__
    print("Passed?", z == res)
    print("Expected: ", res)
    print("Actual  : ", z)
    global total, failed
    total  += 1
    failed += 1 if (z != res) else 0

def work():
    k, n, w = map(int, input().split())
    s = w*(w+1)//2
    print(max(0, s*k-n))

def test():
    run("""3 17 4""", """13""")
    run("""1 2 1""", """0""")

if('LOCALTEST' in os.environ):
    test()
    print("\n Result: %s (%d total, %d failed)" % ("FAILED" if (failed>0) else "PASSED", total, failed))
else:
    work()
