$0 = 0          # ok
$1 = N / K
$1 = $1 + 1     # ng
$2 = $1 - $0    # dif
while $2 > 1
  $3 = $0 + $1
  $3 = $3 / 2   # mid
  $4 = $3 * $3
  $5 = K * N
  $5 = $5 * $3
  $4 = $4 + $5
  $5 = N * N
  if $4 <= $5
    $0 = $3
  end
  if $4 > $5
    $1 = $3
  end
  $2 = $1 - $0
end
$0 = $0 + N
return $0