text: y = 123
  
  y = "Hola Mundo"
  
  def sum(a,b):
      return a+b
  
  print(sum(3,4))
  
  def toUnderscore(word):
      return word.replace(" ", "_")
  
  print(toUnderscore(y))
  
  def changeLetters(string):
      for x in string:
          if(x.isupper()):
              print(x.lower())
          else:
              print(x.upper())
  
  changeLetters(y)
  
  def changeLettersConSwap(string):
      return string.swapcase()
  
  print(changeLettersConSwap(y))