if the date of the instances is between a specific date range count next column

Hi I'm hoping someone will be able to help as this has thrown me.

I'm trying to create a sickness spreadsheet and need help with the formula.

In column A there are a list of dates which the person first became ill and Column B is how many days they had off.

I want to count if the date of the instances is between A1= 01/12/2012 A2= 31/01/2013 how many days did the person have off total?

Can anyone help??

Much appreciated

A sample spreadsheet would be useful