$1=1
$2=2000000000

while$1+1<$2
  $3=$1+$2
  $3=$3/2
  $4=$3+K*2
  if$3>4000000000000000000/$4
    $2=$3
  end
  if$3<=4000000000000000000/$4
    $1=$3
  end
end
$4=$1*N/2000000000
return $4+N