Cumulative Bar Chart

Hi,

I want to create a chart that shows the number of resources active in a month based on start and end date.

I have three columns, Resource Name, Resource Start Date and Resource End Date. The idea is to show a count of resources per month based on the following logic: Their start date is prior to or during the month and end date is within the month or after the last day of the month. So given the following example, the chart should show the following resources as active in January: x(end date is in January), z(started in January) and e. February should show the following resources as active: y,z and e.

How do I build this chart?