First Monday of Year

I am trying to write a function that will display the first Monday of the year based on the user entry.

For example, if I enter;

5/1/2011, It should produce 1/3/2011...
12/31/2012, it should produce 1/2/2012...

etc...



I am sure that this is very easy, however I am having a tough time with this one. Thanks in advance.