Nieuw Knollendam is a very modern town. This becomes clear already when
looking at the layout of its map, which is just a rectangular grid of streets
and avenues. Being an important trade centre, Nieuw Knollendam also has a lot
of banks. Almost on every crossing a bank is found (although there are
never two banks at the same crossing). Unfortunately this has attracted a
lot of criminals. Bank hold-ups are quite common, and often on one day
several banks are robbed. This has grown into a problem,
not only to the banks, but to the criminals as well. After robbing a bank
the robber tries to leave the town as soon as possible, most of the times
chased at high speed by the police. Sometimes two running criminals pass the
same crossing, causing several risks: collisions, crowds of police at
one place and a larger risk to be caught.

To prevent these unpleasant situations the robbers agreed to consult
together. Every Saturday night they meet and make a schedule for the week
to come: who is going to rob which bank on which day? For every day they try
to plan the get-away routes,
such that no two routes use the same crossing. Sometimes they do not
succeed in planning the routes according to this condition, although they
believe that such a planning should exist.

Given a grid of (s*a)
and the crossings where the banks to be robbed are located, find out whether or not it is possible to plan a get-away route from every robbed bank to the city-bounds, without using a crossing more than once.