n = gets.to_i
arr = gets.chomp.split.map(&:to_f).sort
max = 0
arr.each_cons(2){|d, c|
    arr2 = arr.dup
    arr2.delete d
    arr2.delete c
    v = (arr2[-1] + arr2[-2]) / (c - d)
    max = v if max < v
}
puts max
