I want to add a diagonal separating line in a title box of a tabular, but the line doesn't appear (I draw it in red on the picture)
\begin{center}
\begin{tabular}{|l|*{2}{c|}}
\hline
\backslashbox{Mounth}{Year}&2015&2016 \\
\hline
Mai&2560&3610 \\
\hline
June&1465&2985 \\
\hline
\end{tabular}
\end{center}

