how to ungroup a dataset after grouping it to corresponding ids in R

Question

I am setting up a new dataset from grouped data but I am unable to ungroup the data as the code runs and gives the same variables without any changes in the dataframe.

this is the data set I have

s.no     Mno    drug3
   1    100173  9, 3, NA, NA
   2    100463  18, 18, 1, NA, NA, NA
   3    10061   18, 9, 2, 3, NA
   4    101793  0
   5    101876  0
   6    101909  0
   7    102685  0
   8    102707  0
   9    103171  18, 2, 1, NA, NA



A <- B %>% 
      group_by(Mno) %>% 
      summarise(drugs = paste(drug3, collapse=", ")) %>% 
      ungroup(drug3)

I need the output like this

s.no     Mno     drug3
   1    100173     9
   2    100173     3
   3    100173    NA
   4    100173    NA
   5    100463    18
   6    100463    18
   7    100463     1
   8    100463    NA
   9    100463    NA
  10    100463    NA
  11    10061     18
  12    10061      9
  13    10061      2
  14    10061      3
  15    10061     NA
  16    101793     0