P. Prefix Free Code - 2018.9 ECNU ICPC/CCPC Trial Round #2 - ECNU Online Judge

你可以在这里下载。

单点时限: 2.0 sec

内存限制: 512 MB

样例

Input

5 3
a
b
c
d
e
cad

Output

Input

2 2
lubenwei
niubi
lubenweiniubi

Output

NaN

N. Nale Sort O. Oxx Playing Pokemon Go P. Prefix Free Code Q. Query On Tree R. Rabbit's Howse S. Substring Diff T. Transform IP Database U. Ultmaster Dividing The Cake V. Viva La Vida W. Weight Of Subsequence X. X Window Y. You Only Live Once Z. Zerol And KBlack