CONCATENATE rows and copy to specific rows when values change in between different values

Hello

I have a lot of workbooks, which have to be decomposed in the same way.

I have the ollowing code to insert new rows when the value in column B changes and insert text into those rows:

Sub InsertRowsV2()
Dim lastRow As Long
Dim rowPtr As Long
Dim strT1 As String
Dim strT2 As String

strT1 = "Begin-Total"
strT2 = "End-Total"

lastRow = Range("B" & Rows.Count).End(xlUp).Row
Range("B" & lastRow + 1).Value = strT2
For rowPtr = lastRow To 3 Step -1
If Range("B" & rowPtr) <> Range("B" & rowPtr - 1) Then
Range("B" & rowPtr).Resize(2).EntireRow.Insert
Range("B" & rowPtr).Value = strT2
Range("B" & rowPtr + 1).Value = strT1
End If
Next rowPtr

Range("B2").Resize(2, 1).EntireRow.Insert
Range("B2").Resize(2, 1).EntireRow.Interior.ColorIndex = xlNone
Range("B3").Value = strT1

End Sub

However, I now have to CONCATENATE the values between the inserted rows, because in column A I have different numbers, and I have to take the lowest number and the highest number in between those rows and copy paste it to the cell next to the strings (Begin-total and end-total), so that would be in column C in this example.
I have attached a little example...

I have found this code in another tread, however as I wrote, I need it to take the values from the rows between the blank values - this one only take values below the blank cell and paste it above, I need it to both paste it above and below (so the same value appear twice.

Sub Foo()
Dim t As String
Dim M As Long
Dim M2 As Long
Dim Rng As Range, c As Range
Dim Lastrow As Long

M2 = 2
Lastrow = ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Row

Set Rng = Range("A2:A" & Lastrow)
        For Each c In Rng
            If c <> "" Then
            t = t & c & " "
            Else
                If c = "" Then
                M = c.Row
                    If t = "" Then
                    Else
                        t = Left(t, Len(t) - 1)
                        Cells(M2, 1).Value = t
                        t = ""
                        M2 = M
                    End If
                End If
            End If
        Next c
    t = Left(t, Len(t) - 1)
    Cells(M2, 1).Value = t
End Sub

Can anyone help me how to tweak this code to do the job?
Thanks in advance, appreciate any tips.