<?php
  function manen ($sum) {
    if ($sum >= 100000000 && $sum < 1000000000000) return round($sum/100000000, 1)."億円";
    else if ($sum >= 1000000000000) return round($sum/1000000000000, 1)."兆円";
    else if ($sum < 10000) return $sum."円";
    return round($sum/10000, 1)."万円";
  }

  print_r([
    manen(4000),
    manen(27000),
    manen(666098),
    manen(257490303),
    manen(7594923075683)
  ]);
?>