import scala.io.StdIn.{readInt,readLine}

object Main extends App {
  val n = readInt
  val a = readLine.split(" ").map(_.toInt).sorted
  var max = 0D;var ab=0;var cd=0;var r=0D
  for(i<-1 to n-3) {
    cd = a(i) - a(i-1)
    ab = a(n-1)+a(n-2)
    r = ab.toDouble/cd.toDouble
    if(max<r) max = r
  }
  cd = a(n-2)-a(n-3)
  ab = a(n-1)+a(n-4)
  r = ab.toDouble/cd.toDouble
  if(max<r) max = r
  cd = a(n-1)-a(n-2)
  ab = a(n-3)+a(n-4)
  r = ab.toDouble/cd.toDouble
  if(max<r) max = r
  printf("%.5f\n",max)
}