I have a series of month-end values like this:

30/04/2015 31/05/2015 30/06/2015
152 149 154

I also have a separate weekly series. I want a formula that will automatically take the value from the monthly series in the week that most closely matches the month end date. And I want the remaining weeks to stay blank so that I can plot the time-series, connecting the data points with a line.

I want my weekly series to look like this:

19/04/2015 26/04/2015 03/05/2015 10/05/2015 17/05/2015 24/05/2015 31/05/2015
152 149

etc......

Can anyone help me come up with a formula for the weekly data series that will pull out the matching value from the monthly series, but leave the other weekly values blank?

Many thanks