BMI (Body Mass Index) 
 Problem Description 
The body mass
index (BMI) is a measure for human body shape based on an
individual's mass and height.  We want to write a program to calculate
the BMI of a user.
 Specification 
-  Input: mass (in kg) and height (in m).
 -  Output: BMI
 -  Relationship: BMI = mass / (height * height)
 
The program may run as follows.  (Note that the normal value of BMI
should be between 18 and 24.  It seems that Lin Chi-ling is below this
range.)
Please input your mass (in kg) and height (in m) -- 54 1.74
Your BMI is 17.8359