class PockyGame
    attr_reader :l, :k

    def initialize(l: 0, k: 0)
        @l, @k = l, k
    end

    def datainput
        begin
            @l, @k = gets.chomp.split.map { |v| Integer(v) }
        rescue
            
        end
    end

    def pockygame(pocky_length, once_length)
        cnt = pocky_length / (once_length * 2)
        cnt -= 1 if pocky_length % (once_length * 2) == 0
        once_length * cnt
    end

    def dataoutput
        puts pockygame(@l, @k)
    end

    def run
        datainput
        dataoutput
    end
end

if $0 == __FILE__
    PockyGame.new.run
end