Write a R code that transforms data from wide to long format

I am looking for help to transform a data from wide to long format (see attached excel -- the first tab "data_wide" is the original data; the second tab "data_long" is an illustration of how I want the data to look like). Specifically, the original data is at the "store" level; each store has two monthly income vectors, the length of which equals the differences in months between the start and ending month as specified in column D and E. I'd like to transform the data into long format (i.e. time series data), where each row indicates the monthly income for a particular month for a given store. The resulting file should consists of 2,729 rows in total.

The code MUST BE written in R. Please only make an offer if: 1) you have reviewed the excel file and understand the task precisely; 2) you have the R skill to complete the task; 3) the task can be completed within a day. Thank you!