class Calc0222
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @s = args.shift.first
  end

  def run
    stack = []
    @s.scan(/\d+|[+-]/).each do |t|
      case t
      when /\d+/
        t = t.to_i
        loop do
          if stack.empty?
            stack.push(t)
            break
          else
            op = stack.pop
            if stack.last.is_a?(Numeric)
              target = stack.pop
              case op
              when '+'
                stack.push(target - t)
              when '-'
                stack.push(target + t)
              end
              break
            else
              case op
              when '+'
                t = +t
              when '-'
                t = -t
              end
            end
          end
        end
      when '+', '-'
        stack.push(t)
      end
    end
    stack.pop
  end
end

puts Calc0222.new(STDIN.readlines).run if __FILE__ == $0