Strange ice hockey tournament

Forest dwellers, knownto youontaskin "1326. Inthe presentplay hockey..." и "1961. Forestresidents" spend theirstrangetournament, whichisnowknowninmanycircles.It is known thatthe tournamentinvolvedteamskandatthe moment amongallthree teamsare at least twohave not playedwith each other.What is the maximumnumber of matchesmaybe playedat the moment?

Input

A single number- the number ofparticipating teamsk (3 ≤ k ≤ 2000000001).

Output

A single number- the answerto the question posedin the problem.