Arthashastra
तस्य अपि द्वि रथ उत्तरा वृद्धिर् आ एक विंशति रथाद् इति ॥
Two-thirds of the (surplus) chariots may be added to the flanks and the wings, the rest being put in front.
english translation
tasya api dvi ratha uttarA vRddhir A eka viMzati rathAd iti ॥
hk transliteration by Sanscript