conditional update query

I have 2 ms access 2003 tables with the following sample data

table a
id      Floater
1      
2    
3
4


table b
id      Floater
1      N
3      Y

Note: there is only one entry for a given id on both tables
          there may be id entries on table a that are not on table b

I am trying to write an update query that will  update the value of floater on table a

 if there is an matching id entry on table b I would like the value of floater on table a to be set to that on table b


If there is no matching id entry on table b I would like the floater value on table a to be set to N

using the example data I would like table a to have the following values after the update query is run


table a
id      Floater
1      N
2      N
3      Y
4      N