Problems
Buns
Buns
Huseyn likes buns very much, which are sold at ADA University in building C. It is known that
\begin{itemize}
\item you can buy one bun for $a$ qəpiks;
\item you can buy three buns for $b$ qəpiks;
\end{itemize}
Huseyn wants to buy exactly $n$ buns. What is the least number of qəpiks he should spend?
\InputFile
Three positive integers $a, b$ and $n$, each is not greater than $10^9$.
\OutputFile
Print the least amount of qəpiks that Huseyn should spend to buy exactly $n$ buns.
Input example #1
2 5 10
Output example #1
17