def get_minibatch(lines, index, batch_size, word2ind, max_len, add_start=False, add_end=True):
    """Prepare minibatch."""
    if add_start and add_end:
        lines = [
            ['<s>'] + line + ['</s>']
            for line in lines[index:index + batch_size]
        ]
    elif add_start and not add_end:
        lines = [
            ['<s>'] + line
            for line in lines[index:index + batch_size]
        ]
    elif not add_start and add_end:
        lines = [
            line + ['</s>']
            for line in lines[index:index + batch_size]
        ]
    lines = [line[:max_len] for line in lines]

    lens = [len(line) for line in lines]
    max_len = max(lens)

    input_lines = np.array([
        [word2ind[w] if w in word2ind else word2ind['<unk>'] for w in line[:-1]] +
        [word2ind['<pad>']] * (max_len - len(line))
        for line in lines
    ]).astype(np.int32)

    output_lines = np.array([
        [word2ind[w] if w in word2ind else word2ind['<unk>'] for w in line[1:]] +
        [word2ind['<pad>']] * (max_len - len(line))
        for line in lines
    ]).astype(np.int32)

    mask = np.array(
        [
            ([1] * (l - 1)) + ([0] * (max_len - l))
            for l in lens
        ]
    ).astype(np.float32)

    return input_lines, output_lines, lens, mask