#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
using namespace std;
const int oo = 1e9;
int main() {
    int n,m; cin >> n >> m;
    vector<basic_string<int>> adj(n);
    for(int i=0;i<m;++i) {
        int u,v; cin >> u >> v;
        --u,--v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    vector<array<array<int,2>,2>> d(n,{oo,oo,oo,oo});
    vector<array<int,3>> q; q.reserve(n*2);
    auto push = [&](int at, int from, int di) {
        if(d[at][1][0]>di) {
            d[at][1] = {di,from};
            q.push_back({at,from,di});
        }
        sort(d[at].begin(),d[at].end());
    };
    push(0,-1,0);
    for(int i=0;i<q.size();++i) {
        auto [at,from,di] = q[i];
        for(int to : adj[at]) if(to!=from) {
            push(to,at,di+1);
        }
    }
    if(d[0][1][0]==oo) {
        cout << "impossible\n";
    } else {
        int to =0;
        int at = d[0][1][1];
        int di = d[0][1][0]-1;
        vector<int> ans = {0};
        while(at!=-1) {
            ans.push_back(at);
            for(int j=0;j<2;++j) {
                if(d[at][j][0]==di and d[at][j][1]!=to) {
                    to=at;
                    at = d[at][j][1];
                    di--;
                    break;
                }
            }
        }
        cout << ans.size() << '\n';
        for(auto& i : ans) {
            cout << i+1 << ' ';
        }
        cout << '\n';
    }
}