module placticeB
  sub main
    dim input_n as integer
    dim input_str as string
    
    input_n = console.readline()
    input_str = console.readline()
    
    dim input_a() = input_str.split(" ")
    
    dim sum as double = 0.0
    dim count as integer = 0
    while(count < input_n)
      sum += 1/input_a(count) 
      count += 1
    end while
    
    dim result as double = 1/sum
    console.writeline(result)
    
  end sub
end module