Function AccessionRangeEnd() As Integer

    Dim x As Long

    With Sheets("Akcesje")
        x = .Range("F" & .Rows.Count).End(xlUp).row
    End With

    Debug.Print x

    AccessionRangeEnd = x
End Function

Sub cTest()
    Worksheets("Akcesje").Range("K1").FormulaLocal = "=AccessionRangeEnd()"

    Debug.Print "End of cTest()"
End Sub