Find total sum of all the sums

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VB

MS-Excel

I have a data where I have found SUM of some values at some places. The SUM I used in the code was calculated dynamically. I haven't specified the Row or Coulumn, or Range.
So I just want to know now how can I now find the total of all the SUMs I calculated at the end of UsedRange.Rows.Count?

What I have tried:

<pre>For i = 1 To .UsedRange.Rows.Count
        If IsNumeric(.Cells(i, 6).Value) = True And .Cells(i, 6).Value <> "" Then
            If firstnum = "" Then
                firstnum = .Cells(i, 6).Address(False, False)
            End If
            If .Cells(i + 1, 6).Value = "" Then
                lastnum = .Cells(i, 6).Address(False, False)
                i = i + 1
                .Cells(i, 6).Formula = "=SUM(" & firstnum & ":" & lastnum & ")"
                firstnum = ""
            End If

This calculates the SUM of some values entered in D column. The values entered are in irregular pattern, and there's a sum calculated after a block of range ends. So after all such sums, I need a grand sum at the end. The above code calculates the sum finding first number and last number of a block and adds the number in between of them. It will be great if anyone can throw a light on it...
Thanks!!!