#include 
#include 
#include 
#include 
#include 
#include 
#define ll long long
#define ps push_back
using namespace std;
const int maxn = 1e5 + 10;
vector graph[maxn];
bool visited[maxn];
vector cycle;
bool dfs(int node, int parent) {
    visited[node] = true;
    
    for(int i = 0; i < (int) graph[node].size(); i++) {
        int neighbour = graph[node][i];
        cycle.push_back(neighbour);
        
        if(!visited[neighbour]) {
            if(dfs(neighbour, node)) {
                return true;
            }
        }
        else if(neighbour != parent) {
            return true;
        }
        cycle.pop_back();
        
    }
    return false;
}
int main() {
    int n,m;
    cin >>n >> m;
    
    for(int i = 0;i> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
        
    }
    memset(visited, false, sizeof visited);
    for(int i = 1; i <= n; i++) {
        cycle.push_back(i);
        if(!visited[i] and dfs(i, -1)) {
            vector res;
            for(int j = (int) cycle.size() - 1; j >= 0; j--) {
                res.push_back(cycle[j]);
                if(cycle[j] == cycle[(int) cycle.size() - 1] and j != (int) cycle.size() - 1 ) {
                    break;
                }
            }
            cout << res.size() << endl;
            for(int x : res) {
                cout << x << " " ;
            }
            return 0;
        }
        cycle.pop_back();
    }
    cout << "IMPOSSIBLE" << endl;
}