#include <iostream>
#include <map>
#include <vector>
#include <math.h>
#define INF 900000000

using namespace std;

void dfs1(map<string, vector<string>>* g, map<string, int>* color, vector<string>* order, string curr){
    (*color)[curr] = 1;

    for (int i = 0; i < (*g)[curr].size(); i++){
        string to = (*g)[curr][i];

        if ((*color)[to] == 0){
            dfs1(g, color, order, to);
        }
    }

    (*order).push_back(curr);
    (*color)[curr] = 2;
}

void dfs2(map<string, vector<string>>* g, map<string, int>* component, int componentNo, string curr){
    (*component)[curr] = componentNo;

    for (int i = 0; i < (*g)[curr].size(); i++){
        string to = (*g)[curr][i];

        if ((*component)[to] == -1){
            dfs2(g, component, componentNo, to);
        }
    }
}

int main(){
    int n, m;
    cin >> n >> m;

    map<string, vector<string>> graph;
    map<string, vector<string>> reversedGraph;
    map<string, int> components;
    map<string, int> color;

    vector<string> guests;
    vector<string> order;

    for (int i = 0; i < n; i++){
        string s;
        cin >> s;

        guests.push_back(s);

        graph['-' + s] = vector<string>(0);
        graph['+' + s] = vector<string>(0);

        reversedGraph['-' + s] = vector<string>(0);
        reversedGraph['+' + s] = vector<string>(0);

        color['-' + s] = 0;
        color['+' + s] = 0;

        components['-' + s] = -1;
        components['+' + s] = -1;
    }


    for (int i = 0; i < m; i++){
        string from, to;
        cin >> from >> to >> to;

        graph[from].push_back(to);
        reversedGraph[to].push_back(from);

        if (from[0] == '-')
            from[0] = '+';
        else
            from[0] = '-';

        if (to[0] == '-')
            to[0] = '+';
        else
            to[0] = '-';

        graph[from].push_back(to);
        reversedGraph[to].push_back(from);
    }


    for (int i = 0; i < n; i++){
        if (color['-' + guests[i]] == 0){
            dfs1(&graph, &color, &order, '-' + guests[i]);
        }

        if (color['+' + guests[i]] == 0){
            dfs1(&graph, &color, &order, '+' + guests[i]);
        }
    }


    int cmp = 0;

    for (int i = 0; i < order.size(); i++){
        string vert = order[order.size() - 1 - i];

        if (components[vert] == -1){
            cmp++;
            dfs2(&reversedGraph, &components, cmp, vert);
        }
    }

    bool isCycle = false;
    vector<string> answer;

    for (int i = 0; i < guests.size(); i++){
        if (components['-' + guests[i]] == components['+' + guests[i]]){
            isCycle = true;
            break;
        }
        else{
            if (components['+' + guests[i]] < components['-' + guests[i]]){
                answer.push_back(guests[i]);
            }
        }
//        cout << endl;
//        cout << '-' + guests[i] << " " << components['-' + guests[i]] << endl;
//        cout << '+' + guests[i] << " " << components['+' + guests[i]] << endl;
//        cout << endl;
    }

    if (!isCycle && answer.size() != 0){
        cout << answer.size() << endl;
        for (int i = 0; i < answer.size(); i++){
            cout << answer[i] << endl;
        }
    }
    else{
        cout << -1;
    }
}