text: # transcribing DNA into RNA
  
  DNA_seq = str(input("Input DNA-sequence: "))
  DNA_seq = str.upper(DNA_seq)
  
  
  RNA_complement = ""
  n = len(DNA_seq) - 1
  while n >= 0:
      if DNA_seq[n] == "A":
          RNA_complement += "A"
          n = n - 1
      elif DNA_seq[n] == "T":
          RNA_complement += "U"
          n = n - 1
      elif DNA_seq[n] == "C":
          RNA_complement += "C"
          n = n - 1
      elif DNA_seq[n] == "G":
          RNA_complement += "G"
          n = n - 1
      else:
          print("Abbruch! Fehlerhafte Eingabe")
          break
  
  print("output:   " + RNA_complement[::-1])  # [::-1] for reverse output
  