class Calc0149
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @aw, @ab = args.shift.map(&:to_i)
    @bw, @bb = args.shift.map(&:to_i)
    @c, @d = args.shift.map(&:to_i)
  end

  def run
    w1 = [0, @c - @ab].max
    w2 = [@d, @bw + w1].min
    @aw - w1 + w2
  end
end

puts Calc0149.new(STDIN.readlines).run if __FILE__ == $0