require 'enumerator'
require 'pp'

num_teams = ARGV.first.to_i
teams = *1..num_teams
games = teams.combination(2).to_a
slots = Array.new(num_teams-1) { [] }
taken = Array.new(num_teams-1) { [] }
games.each { |a,b|
  slots.each_with_index { |slot, i|
    unless taken[i][a] || taken[i][b]
      slot << [a,b]
      taken[i][a] = true
      taken[i][b] = true
      break
    end
  }
}

p *slots