input: Write a python function to format a given string to an email address.
  assert format_string("John Doe jdoe@example.com") == "John Doe <jdoe@example.com>"
  assert format_string("Jane Smith janesmith@example.org") == "Jane Smith <janesmith@example.org>"
  assert format_string("Alice Johnson alice.johnson@example.net") == "Alice Johnson <alice.johnson@example.net>"
output: def format_string(s):
      parts = s.split()
      name = " ".join(parts[:-1])
      email = parts[-1]
      return f"{name} <{email}>"