great problem!
i really enjoyed the time i spent to finding the o(n)
solution...
but now i'm thinking whether it was suitable to the trial
tour of the Ural Championship... if i were at that
championship, i would fail to solve it...
Yeah, it's quite easy - i mean, the solution is very
simple, but it took me much time to find it... And most
problems of the trial tour must be easily solved in 20
minutes.
And here... only 23 teams were able to solve...

> great problem!
> i really enjoyed the time i spent to finding the o(n)
> solution...
> but now i'm thinking whether it was suitable to the trial
> tour of the Ural Championship... if i were at that
> championship, i would fail to solve it...
Only one (of 33) team has solved this problem. We had not
much experience that time :)