Program Structure

Your program should have the following form:

PROGRAM    program-name
   IMPLICIT   NONE
   [specification part]
   [execution part]
   [subprogram part]
END PROGRAM program-name

Here are some addition notes:

Contents in [ ] are optional.
Keyword IMPLICIT NONE must present.
A program starts with the keyword PROGRAM,

followed by a program name,
followed by the IMPLICIT NONE statement,
followed my some specification statements,
followed by the execution part,
followed by a set of internal subprograms,
followed by the keywords END PROGRAM and the program name.

For improving readability, your program should add comment lines.