Programs must be in a single source file with the name specified in the problem description; failure to meet this requirement is a "Syntax or Compilation Error".
A note to Java programmers: You can still have more than one top-level classes in a single source file as long as only the main one is declared public while the rest are unqualified (i.e. just 'class', without 'public').
Your program cannot require any intervention from the user. All input must be read from the input file.
If you submit a program that requires user intervention, you'll most probably receive a "Time-Limit Exceeded" error.
Contestants who have the habit of placing a "press any key to continue" statement at the end of their program should pay attention to this point.
Make sure your program will compile and run using the Judges environment. Use the PC^2 test button.
The PC^2 section of the RuleBook includes more helpful hints.