Adding a number to a cell on the first of the month

I am using excel to keep track of leave time at my work, each month I have to add the time that we get for that month. I need a formula or something to put a number in a cell on the first of each month. Example I need to put the number 8 in cell E5 on the first day of the month the next month I need 8 in E6 and so on.
Thanks for your help. Paul