Conditional Formatting help....formula based...

Hello,

I need help on conditional formatting. In coloumn "P" in my excel sheet I want to apply conditional formating where if that sum total does not exceed or is less than the total of columns "A + B + C +D". I would like the colour to highlight when it does exceed or less than those amounts in red....can anyone help me. It is a newbie question and appreciate if someone can help me so I can learn and get better in excel...thanks...