Shading cells based on entries across rows

Morning all,

Here's one for you:

I have a spreadsheet I use for my payroll. In column C I input the total hrs done by my staff. What I want to do is highlight the cells in red that contain no figures. That I can do, but I don't want it to highlight that cell if the adjacent cells in rows K L M contain numbers, these rows are where I enter a number if sick or maternity etc.

Any advice on how to do this as I want to apply the format to all 64 rows (amount of staff I look after)

Thanks
Lew