#include <iostream>
#include <map>
#include <string>
#include <algorithm>
using namespace std;
map<string, int> Mp;
int N,M,Cnt;
string a;
string ar[550000];
int main()
{
cin>>N>>M;
for(int x=0; x<N+M; x++)
{
cin>>a;
Mp[a]++;
}
map <string, int> ::iterator iter;
for(iter = Mp.begin(); iter !=Mp.end(); iter++)
{
if(iter->second == 2)
{
ar[Cnt++]=iter -> first;
}
}
cout<<Cnt<<endl;
sort(ar,ar+Cnt);
for(int x=0; x<Cnt; x++) cout<<ar[x]<<endl;
}