Problems
Stack push / pop
Stack push / pop
Simulate the operations with the stack:
\begin{itemize}
\item \textbf{push x} --- insert value $x$ into the stack;
\item \textbf{pop} --- delete the top element;
\item \textbf{top} --- print the top element (without deleting it);
\end{itemize}
All \textbf{pop} commands are correct.
If stack is empty and \textbf{top} command arrives, print nothing.
\InputFile
Each line contains a single command.
\OutputFile
For each \textbf{top} command print on a separate line the corresponding result.
Input example #1
push 5 push 2 top pop top pop top push 7 top
Output example #1
2 5 7