#include <iostream>
#include <fstream>
using namespace std;

int lm,a[2048],b[2048],c[500],d[500],n,m;

int main(){
    ifstream f("cmlsc.in");
    ofstream g("cmlsc.out");
    f >>n>>m;
    for(int i = 1; i<=n; ++i){
        f>>a[i]; c[a[i]]++;}
    for(int j = 1; j<=m; ++j){
f>>b[j];d[b[j]]++;}
for(int i=1;i<=257; ++i)
if(c[i]==d[i])
lm+=c[i];
else if(c[i]>d[i])
lm+=d[i];
else lm+=c[i];
g<<lm<<endl;
for(int i=1; i<=257; ++i)
if(c[i]==d[i])
while(c[i])g<<i<<" ",c[i]--;
else if(c[i]>d[i])
while(d[i])g<<i<<" ",d[i]--;
else while(c[i])g<<i<<" ",c[i]--;
return 0;}