def group_iban(string):
    """
    Split IBAN to have space after every fourth character.
    e.g. 1111 1111 1111 1111 11
    :param string: input string
    :return: modified string
    """
    string = ''.join(string.split())
    return ''.join(e if (i+1) % 4 else e+" " for (i,e) in enumerate(string)).strip()