input: Write a python function to concatenate two strings.
  assert concatStrings('Hello', 'World') == 'HelloWorld'
  assert concatStrings('foo', 'bar') == 'foobar'
  assert concatStrings('Python', 'Programming') == 'PythonProgramming'
output: def concatStrings(str1, str2):
      return str1 + str2