Exercise: Connect Four |2|
~~~~~~~~~~~~~~~~~~~~~~~~~~

Connect Four is a popular board game which is played by two players. In
this game, players take a colored discs (red for one player, yellow for
another) and drop them into a column in a suspended grid. The discs fall
down until there are no available space left in the column. If any of
the players form a diagonal, horizontal or vertical line with four of
the players discs, player wins.

Write a program that determines for a given board state whether there is
a winner or not. The game grid is always :math:`N\times N`,
:math:`N \ge 4`. :math:`N` is given in the first input line. In the
following :math:`N` lines the board configuration is given row by row,
represented as strings with :math:`N` elements each. The elements are
``’R’`` for red, ``’Y’`` for yellow and ``’.’`` for empty.

Print ``"yes"`` if there is a winner, ``"no"`` if not.

.. container:: sampleio

   Sample I/O:

.. |2| image:: ../../figures/difficulty_four.png
   :class: difficulty

.. code:: default

   Input:
   4
   YRYR
   RYRY
   YRYR
   RYRY

   Output:
   yes


   Input:
   4
   RY..
   YYYR
   RYRY
   YRRY


   Output:
   no