Function for grading in RDLC report

I am having this function in my rdlc report but i run the report the moment it reaches the ranges of 65 it does not show the corresponding grade

Public Function grading(tt) As String
    if IsNothing(tt) then
        grading = Nothing
        Exit Function
    end if

    tt = int(tt)
   
    if (tt >= 0 and tt <= 44) then
                grading = "E"
    else 
            if (tt > 45 and tt <= 54) then
                grading = "D"
    else 
            if (tt > 55 and tt <= 64) then
                grading = "C"
    else 
          if (tt > 65 and tt <= 79) then
                grading = "B"
    else 
            if (tt > 80 and tt <= 100) then
                grading = "A" 
    end if
end if
end if
end if
end if
End Function

please help