Snacks

Dongsu wants to buy snacks at a bakery. When his own money is not enough, he gets the difference from his parents. One snack costs $K$ won, he wants $N$ snacks, and he currently holds $M$ won.

The snacks cost $K \times N$ won in total. If that total is larger than $M$, he has to get the difference $K \times N - M$ won from his parents, and if $M$ is at least the total, he gets nothing. For example, buying 4 snacks at 30 won each while holding 100 won needs 20 won, and buying 6 snacks at 20 won each while holding 120 won needs nothing.

Given $K$, $N$, and $M$, find how much money Dongsu has to get from his parents.

The first line contains the price of one snack $K$, the number of snacks $N$, and the money Dongsu holds $M$, separated by spaces. All three are integers with $1 \le K, N \le 1000$ and $1 \le M \le 100000$.

Print on the first line the amount Dongsu has to get from his parents. Print 0 when he needs nothing.