extracting a single list of names with a formula

Hi,

I have a long list of names in A2:A1000 in Sheet1 and another list of names in A2:A1500 in Sheet2.

When the data in these ranges is updated each month the last name may be above or below cell A1000 in Sheet1 and above or below cell A1500 in Sheet2.

Each name occurs only once in each sheet but any name may appear in both Sheet1 and in Sheet2.

In cell A2 and below in Sheet3 I would like to create a formula that will return a single instance of each item in both Sheet1 and Sheet2.

Can someone please suggest a solution - I would like to use a formula rather than a filter, please.

Thanks!