#include <bits/stdc++.h>
#include "optimization.h"

using namespace std;

const int MAXN = 1e4;

long long len[4194310][25];
int edge[25];

vector <int>

int test(){

};

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int n, m;
    cin >> n >> m;

    for (int i = 0; i < 23; i++) {
        edge[i] = 0;
       // edge[i] = edge[i] | (1 << i);
    }

    int u, v;
    for (int i = 0; i < m; i++) {
        cin >> u >> v;
        u--;
        v--;
        if (u != v)
        edge[u] = edge[u] | (1 << v);

    }

    for (int A = 0; A < (1 << n); A++) {
        for (int i = 0; i < n; i++) {
            len[A][i] = 0;
        }
    }


    for (int A = 0; A < (1 << n); A++) {
        for (int x = 0; x < n; x++) {

            if (!((A >> x) & 1)) { // x - добавляемый элемент
                for (int j = 0; j < n; j++) {
                    if ((A >> j) & 1) { // элемент j в мн-ве
                        if ((edge[j] >> x) & 1) { //есть ребро
                           // cout << A <<' '<< j <<' ' <<x <<  endl;
                            len[A | (1 << x)][x] = max(len[A | (1 << x)][x] ,len[A][j] + 1);
                        }
                    }
                }
            }
        }
    }

    long long ans = 0;
    long long finish;
    long long temp_A;
    for (int A = 0; A < (1 << n); A++) {
        for (int i = 0; i < n; i++) {
            if (len[A][i] > ans) {
                temp_A = A;
                ans = len[A][i];
                finish = i;
            }
        }
    }

    cout << ans << endl;
    long long bit_path = 0;
    vector <long long> path;
    for (int i = 0; i < ans; i++) {

        for (int i = 0; i < n; i++) {
            if (len[(temp_A & ~(1 << finish))][i] + 1 == len[temp_A][finish] && ((edge[i] >> finish) & 1) && !((bit_path >> i) & 1)) {
                bit_path = bit_path | (1 << finish);
                temp_A = (temp_A & ~(1 << finish));
                //cout << bit_path << ' ' << temp_A << ' ' <<  finish;
                path.push_back(finish+1);
                finish = i;
                break;
            }
        }

    }
    path.push_back(finish+1);
    reverse(path.begin(),path.end());
    for (int i = 0; i <= ans; i++) {
        cout << path[i] << ' ';
    }
}