问题 A: Alive Fossils

链接：https://ac.nowcoder.com/acm/contest/57362/A
来源：牛客网
Nowcoder Multi-University Training Camp is now holding again. As a contestant, you are a little bit curious about the problem setters. Now you have a list of the problem setters among all the $n$ Nowcoder Multi-University Training Camps, and you are curious about the alive fossil setters, who set problems in all the $n$ camps. Please output the alive fossil setters in the lexicographic order.

The first line contains one integer $n$ (1≤n≤1051\le n \le 10^51≤n≤105), denoting the number of Nowcoder Multi-University Training Camps ever held.
For each training camp:
The first line contains one integer $c$ (1≤c≤1051 \le c \le 10^51≤c≤105), denoting the number of problem setters.
Each of the following $c$ lines contains a string containing lowercase letters and digits only, denoting a problem setter in the camp. No problem setters appear more than once in a training camp.
It is guaranteed the total length of strings in all training camps does not exceed 10610^6106.

Output a single integer $f$ in the first line, and then output all the $f$ alive fossil setters in the lexicographic order in the following $f$ lines.

2
14
buaa
bit
sunsiyu
uestc
ezec
qcjjfanclub
nfls
oscar114514
jianglyfan
gromah
calabash
lzr010506
gispzjz
roundgod
13
uestc
bit
buaa
gispzjz
roundgod
ynoi
hdu
oscar114514
gromah
calabash
quailty
nfls
sjtu

9
bit
buaa
calabash
gispzjz
gromah
nfls
oscar114514
roundgod
uestc