Option Explicit
Sub main()
MsgBox getString(Range("G11, K12, G13, G14, G15, G16, K17, G18, G19, G20, K21"))
End Sub
Function getString(ByRef rng As Excel.Range) As Variant
Dim c As Excel.Range
Dim vRet As Variant
For Each c In rng
vRet = vRet & c.Value & "-"
Next
Do While InStr(1, vRet, "--", vbBinaryCompare) > 0
vRet = Replace(vRet, "--", "-")
Loop
getString = Left(vRet, Len(vRet) - 1)
End Function