Problem:
Reverse Polish notation is a notation where every operator follows all of its operands. For example, an expression (1+2)*(5+4) in the conventional Polish notation can be represented as 1 2 + 5 4 + * in the Reverse Polish notation. One of advantages of the Reverse Polish notation is that it is parenthesis-free.

Write a program which reads an expression in the Reverse Polish notation and prints the computational result.

An expression in the Reverse Polish notation is calculated using a stack. To evaluate the expression, the program should read symbols in order. If the symbol is an operand, the corresponding value should be pushed into the stack. On the other hand, if the symbols is an operator, the program should pop two elements from the stack, perform the corresponding operations, then push the result in to the stack. The program should repeat this operations.

Input

An expression is given in a line. Two consequtive symbols (operand or operator) are separated by a space character.

You can assume that +, - and * are given as the operator and an operand is a positive integer less than 106

Output

Print the computational result in a line.

Constraints

2 ≤ the number of operands in the expression ≤ 100

1 ≤ the number of operators in the expression ≤ 99

-1 × 109 ≤ values in the stack ≤ 109

Sample Input 1

1 2 +

Sample Output 1

3

Sample Input 2

1 2 + 3 4 - *

Sample Output 2

-3

Notes

Template in C

Solution in Ruby (judge verdict: Accepted)


class Stack
  def initialize
    @sz = 0
    @elem = []
  end

  def push obj
    @elem << obj
    @sz += 1
  end

  # returns obj or nil if the stack is empty
  def pop
    obj = @elem.last
    @sz -= 1 if @sz > 0
    @elem = @elem[0..-2]
    obj
  end

  def peak
    obj = @elem.last
    obj
  end
end

def main
  str = gets
  exp = str.chomp.split(/\s/)
  stack = Stack.new
  exp.each do |elem|
    if operator? elem
      oprand2 = stack.pop
      oprand1 = stack.pop
      stack.push(evaluate(elem, oprand1, oprand2))
    else
      stack.push elem
    end
  end
  puts stack.pop
end


def operator? str
  str == "+" or str == "-" or str == "*" or str == "/"
end

def evaluate(op,oprand1,oprand2)
  num1 = oprand1.to_i
  num2 = oprand2.to_i
  res = case op
        when "+"
          num1 + num2
        when "-"
          num1 - num2
        when "*"
          num1 * num2
        when "/"
          num1 / num2
        end
  res
end


main