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)

#!/usr/bin/ruby
# -*- coding: utf-8 -*-
=begin
ALDS1_3-A

Elementary data structures - Stack
=end

class Rpc
  def initialize(f)
    @a = Array.new(f.length)
    0.upto(f.length-1).each{|i| @a[i] = f[i]}

  end

  def calc()
    st = []
    val=0
    while @a.length > 0 do
      x = @a.shift
      if x =~ /\d+/ then
        st.push x.to_i
      elsif x == "+" then
        st.push(  st.pop + st.pop)
      elsif x == "-" then
        st.push( -st.pop + st.pop)
      elsif x == "*" then
        st.push(  st.pop * st.pop)
      else
        abort "unknown:#{x}"
      end
    end
    st.pop
  end

end

class Main
  def initialize()
    #fh = open("x.txt")
    fh = STDIN
    f = fh.gets.chomp.split
    rp = Rpc.new(f)
    puts rp.calc()
  end
end

if $0==__FILE__ then
  Main.new()
end