input: Write a function to search for a given word in a large document and return the line number where the word is found. If the word is not found, return -1.
  assert findWord('This is the first line of the document.\nThis is the second line of the document.\nThis is the third line of the document.', 'second')==2
  assert findWord('This is the first line of the document.\nThis is the second line of the document.\nThis is the third line of the document.', 'fourth')==-1
  assert findWord('This is the first line of the document.\nThis is the second line of the document.\nThis is the third line of the document.', 'line')==1
  assert findWord('This is the first line of the document.\nThis is the second line of the document.\nThis is the third line of the document.', 'third')==3
  assert findWord('', 'word')==-1
output: def findWord(document, word):
      lines = document.split('\n')
      for i, line in enumerate(lines):
          if word in line:
              return i + 1
      return -1