Rails |
There is a famous railway station in PopPush City. Country there is incredibly hilly. The station was built in last century. Unfortunately, funds were extremely limited that time. It was possible to establish only a surface track. Moreover, it turned out that the station could be only a dead-end one (see picture) and due to lack of available space it could have only one track.
The local tradition is that every train arriving from the direction A
continues in the direction B with coaches reorganized in some way. Assume that
the train arriving from the direction A has coaches numbered in increasing order
. The chief for
train reorganizations must know whether it is possible to marshal coaches
continuing in the direction B so that their order will be
. Help him and
write a program that decides whether it is possible to get the required order of
coaches. You can assume that single coaches can be disconnected from the train
before they enter the station and that they can move themselves until they are
on the track in the direction B. You can also suppose that at any time there can
be located as many coaches as necessary in the station. But once a coach has
entered the station it cannot return to the track in the direction A and also
once it has left the station in the direction B it cannot return back to the
station.
The last block consists of just one line containing 0.
5 1 2 3 4 5 5 4 1 2 3 0 6 6 5 4 3 2 1 0 0
Yes No Yes