#include <bits/stdc++.h>
#define f(i, s, k, l) for (int i = s; i < k; i += l)
#define for0(i, k) f(i, 0, k, 1)

#define pl pair<long long, long long>
#define pb push_back

#define vl vector<long long>
#define vi vector<int>
#define sz(x) (ll)(x).size()

using namespace std;
using ll = long long;
using ld = double;

void getPath(vl &trip, vector<vl> &adj, vl &parent, ll v) {
    ll cur = v;
    while (parent[cur] != cur) {
        trip.pb(cur);
        cur = parent[cur];
    }
    trip.pb(cur);
}

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

    ll n, m, u, v;
    cin >> n >> m;
    vector<vl> adj(n);
    for0(i, m) {
        cin >> u >> v;
        u--;
        v--;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    vl dist(n, 1e9);
    vl parent(n, -1);
    dist[0] = 0;
    parent[0] = 0;
    ll res = 1e9, v1 = -1, v2 = -1;
    queue<ll> q;
    q.push(0);
    while (!q.empty()) {
        ll cur = q.front();
        q.pop();
        for (ll neigh : adj[cur]) {
            if (parent[neigh] == -1) {
                q.push(neigh);
                parent[neigh] = cur;
                dist[neigh] = cur + 1;
            }
            else if (neigh == parent[cur]) continue;
            else if (dist[neigh] + 1 + dist[cur] < res) {
                    res = dist[neigh] + 1 + dist[cur];
                    v1 = cur;
                    v2 = neigh;
                }
            }
        }
    if (v1 == -1) {
        cout << "impossible" << endl;
        return 0;
    }
    vl trip;
    getPath(trip, adj, parent, v1);
    reverse(trip.begin(), trip.end());
    getPath(trip, adj, parent, v2);


    cout << sz(trip) << endl;
    for (ll x : trip) cout << x + 1 << endl;
}