#include <iostream>
#include <algorithm>
#include <iterator>
#include <stdio.h>

using namespace std;

string team[16]; int teamLen = 0;
string tmpTeam[16]; int tmpTeamLen = 0;

bool nums[16] = {false};
int n = 0, k = 0;
bool rejectedPlayers[16];

bool isValid(string txt, string occ[][2]);
void getTeam (string namesT[], string occ[][2], int start, int depth);

int main()
{
    scanf("%d %d", &n, &k);
    string namesT[16];
    string occ[16][2];

    for(int i = 0; i < n; i++)
        cin >> namesT[i];

    for (int i = 0; i < k; i++)
        cin >> occ[i][0] >> occ[i][1];

    if (k != 0)
    {
        getTeam (namesT, occ, 0, 1);
        printf("%d \n", tmpTeamLen);
        for (int i =0; i < tmpTeamLen; i++)
        {
            cout << tmpTeam[i] << "\n";
        }
    }
    else
    {
        printf("%d \n", n);
        for (int i =0; i < n; i++)
        {
            cout << namesT[i] << "\n";
        }
    }
    return 0;
}

void getTeam (string namesT[], string occ[][2], int start, int depth)
{
    if (depth == n)
    {
        if (teamLen >= tmpTeamLen)
        {
            std::copy(team, team + teamLen, tmpTeam);
            tmpTeamLen = teamLen;
        }
        teamLen = 0;
        return;
    }

    for (int i = start; i < n; i++)
    {
        if (nums[i]) continue;
        nums[i] = true;
        if (isValid(namesT[i], occ))
        {
            string txt = namesT[i];
            team[teamLen++] = txt;
            getTeam(namesT, occ, i, depth+1);
        }
        nums[i] = false;
    }
}

bool isValid(string txt, string occ[][2])
{
    bool flag = true ;
    string a = txt; int b = -1;

    for (int i = 0; i < k && flag; i++)
    {
        if (occ[i][0] == txt)
        {
            for (int j = 0; j < teamLen; j++)
            {
                if (team[i] == occ[i][1])
                {
                    b = 1;
                    break;
                }
            }
        }
        else if (occ[i][1] == txt)
        {
            for (int j = 0; j < teamLen; j++)
            {
                if (team[i] == occ[i][0])
                {
                    b = 1;
                    break;
                }
            }
        }
        if (b != -1) flag = false;
    }

    return flag;
}