def make_markdown_url(line_string, s):
    """
    Turns an URL starting with s into
    a markdown link
    """
    new_line = []
    old_line = line_string.split(' ')
    for token in old_line:
        if not token.startswith(s):
            new_line.append(token)
        else:
            new_line.append('[%s](%s)' % (token, token))
    return ' '.join(new_line)