class Sugoroku
  @@memo={"1"=>1, "2"=>2}

  def self.comb(grid)
    return @@memo[grid.to_s] if @@memo[grid.to_s]
    return @@memo[grid.to_s] = comb(grid - 2) + comb(grid - 1)
  end
end

n=gets.to_i
p Sugoroku.comb(n)