arr = [5, 3, 4, 3, 5, 5, 3]


a = arr.group_by{ |e| e }.select { |k, v| v.size > 2 }.map(&:first)
b = arr.group_by{ |e| e }.select { |k, v| v.size < 2 }.map(&:first)

if a.any? && b.aby?
    puts b.inspect
else
    return -1
end