Postfix expressions are arithmetical expressions
where the operators come after anything they operate
on. Postfix is important because it maintains precedence
without the use of (), and they're "easy" to evaluate.
In this problem, you get to see how "easy" postfix
expressions are to evaluate.
Input:
Each line of the input will be no more than 80 characters
and will contain one expression
to be evaluated. All expressions will be correct
postfix expressions. There will be one space between
each number/operator. The only operators we're interested
in is + (addition), - (subtraction), and * (multiplication).
There is no division. All numbers are non-negative integers.
Output:
Your program is to output the result of evaluting the epxression.
Note that while the input numbers will not be negative, the answer
may be negative.