输入

5 2
abcde
abcde

正确输出

1
abcde

被叉掉的：

• https://www.luogu.com.cn/blog/lty26319/solution-p4045
• https://www.luogu.com.cn/blog/Tony-ZhuJialiang/ti-xie-p4045-jsoi2009-mi-ma
• https://flyinthesky.blog.luogu.org/solution-p4045