To get the length of each line in the file text, use the length function.
若要获取文件中每行文本的长度，请使用length函数。
For each box sequence in the input file, output the length of the longest nesting string on one line followed on the next line by a list of the boxes that comprise this string in order.
对应输入的每个盒子序列，应在第一行输出最长的嵌套串长度，在下一行按顺序输入组成这个嵌套串的盒子列表。
The output file should contain a single line with a single integer that represents the length of the longest theme.
输出文件应只含一个整数，即最长主题的长度。
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