def solve
  stack = []
  A.each do |a|
    case a
    when /\d+/
      stack << a.to_i
    when '+'
      a = stack.pop
      b = stack.pop
      stack << b + a
    when '-'
      a = stack.pop
      b = stack.pop
      stack << b - a
    end
  end
  stack.pop
end

N = gets.to_i
A = gets.chomp.split

puts solve