#include <iostream>
#include <utility>
#include <vector>

int main(){
    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int>> g(n);
    std::vector<std::pair<int, int>> es(2*m);
    for (int i = 0; i < 2*m; i += 2){
        std::cin >> es[i].first >> es[i].second;
        es[i+1].second = --es[i].first;
        es[i+1].first = --es[i].second;
        g[es[i].first].push_back(i);
        g[es[i].second].push_back(i+1);
    }
    std::vector<int> prev(2*m, -1), done(n, -1), todo = g[0];
    for (int i = 0; i < todo.size(); ++i){
        int ei = todo[i];
        int from = es[ei].first, to = es[ei].second;
        if (to == 0){
            std::vector<int> solution;
            for (int j = ei; ; j = prev[j]){
                solution.push_back(j);
                if (es[j].first == 0) break;
            }
            std::cout << solution.size() + 1 << std::endl << '1';
            for (int j = solution.size() - 1; j >= 0; --j) std::cout << ' ' << es[solution[j]].second + 1;
            std::cout << std::endl;
            return 0;
        }
        if (done[to] == -1){
            for (int j : g[to]){
                if (es[j].second != from){
                    todo.push_back(j);
                    prev[j] = ei;
                }
                else done[to] = j;
            }
        }
        else if (done[to] >= 0){
            todo.push_back(done[to]);
            prev[done[to]] = ei;
            done[to] = -2;
        }
    }
    std::cout << "impossible" << std::endl;
    return 0;
}