def third_root(q)
  x = q / 2.0
  
  x -= (x ** 3 - q) / (3 * x ** 2) while (x ** 3 - q).abs > 0.00001 * q
  
  return x
end

while true
  q = gets.to_i
  
  break if q == -1
  
  puts third_root(q)
end