Right hand notes have too many ledger lines.

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This is the code:

\version "2.12.3"
\score {
    \new PianoStaff <<
        \set PianoStaff.midiInstrument = "acoustic grand"
        \tempo 4 = 120
        \new Staff {
            \relative c' {
                c d c b
                a c d c
                c d c b
                g c d c
            }
        }

        \new Staff {
            \clef "bass"
            \relative c {
                g c e c
                f, a c a
                g c e c
                f, a c a
            }
        }
    >>
    \midi { }
    \layout{ }
}

I have attached the PDF output with this email. In his score, the
treble clef is supposed to be played with right hand and the bass clef
with left hand. However, in the treble clef (right hand), we have two
notes ('a' and 'g') which are below the middle C and thus represented
by extra ledger lines.

Unfortunately, there are too many of these in the music I am writing
and the score is full of too many ledger lines. What is the
recommended way of writing scores like these?

Could you please modify this code to the recommended style so that I
can learn the right way to do this?

ledger.pdf
Description: Adobe PDF document