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

int n, m;
std::vector<std::vector<int>> g;

std::vector<int> d, p;
int a, b, s = 10000000;
bool dfs(int from, int to){
    p[to] = from;
    d[to] = from == -1 ? 1 : d[from] + 1;
    bool retval = false;
    for (int i : g[to]) if (i != from){
        if (d[i] == -1) retval = dfs(to, i) || retval;
        else if (d[to] + d[i] < s) a = to, b = i, s = d[to] + d[i], retval = true;
    }
    return retval;
}

int main(){
    std::cin >> n >> m;
    g = std::vector<std::vector<int>>(n+1);
    for (int i = 0; i < m; ++i){
        int u, v;
        std::cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    d = std::vector<int>(n+1, -1);
    p = std::vector<int>(n+1, -1);
    if (!dfs(-1, 1)){
        std::cout << "impossible" << std::endl;
        return 0;
    }
    std::cout << d[a] + d[b] << std::endl << '1';
    std::vector<int> solution;
    for (int i = a; i != 1; i = p[i]) solution.push_back(i);
    std::reverse(solution.begin(), solution.end());
    for (int i = b; i != -1; i = p[i]) solution.push_back(i);
    for (int i : solution) std::cout << ' ' << i;
    std::cout << std::endl;
    return 0;
}