#include <bits/stdc++.h>
using namespace std;
vector<int> edges[100001];
vector<int> v;
vector<int> visited(100001,0);
void dfs(int i, int prev)
{
    visited[i]=1;
    for(int j:edges[i])
    {
        if(visited[j]==0)
        {
            v.push_back(j);
            dfs(j,i);
        }
        else if(j!=prev && prev!=0)
        {
            vector<int> ans;
            int index;
            for(int k=0;k<(int)v.size();k++)
            {
                if(v[k]==j)
                {
                    index=k;
                    break;
                }
            }
            for(int k=index;k<(int)v.size();k++)
                ans.push_back(v[k]);
            ans.push_back(j);
            cout<<ans.size()<<"\n";
            for(auto &i1:ans)
                cout<<i1<<" ";
            exit(0);
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        int a, b;
        cin >> a >> b;
        edges[a].push_back(b);
        edges[b].push_back(a);
    }
    for(int i=1;i<=n;i++)
    {
        if(visited[i]==0)
        {
            v.push_back(i);
            dfs(i, 0);
            v.clear();
        }
    }
    cout<<"IMPOSSIBLE";
    return 0;
}