#include <bits/stdc++.h>

using namespace std;

typedef int64_t ll;
#define For(i, a, b) for(ll i = a; i <= b; i++)

ll n, m, valid, num[100010];
vector <ll> edge[100010], res;

void dfs(ll u)
{
    for(ll v: edge[u])
    if (edge[v].size() > 1 && !num[v])
    {
        num[v] = num[u] + 1;
        dfs(v);
        if (valid && *res.end() != *res.begin())
        {
            res.push_back(v);
            return;
        }
        num[v] = 0;
    }
    else
    if (num[u] - num[v] > 2 && res.empty())
    {
        valid = v;
        res.push_back(v);
        res.push_back(u);
        return;
    }
}

void process()
{
    For(i, 1, n)
        if (!num[i] && res.empty())
        {
            num[i] = 1;
            dfs(i);
        }
    if (res.empty())
        cout << "IMPOSSIBLE" << "\n";
    else
    {
        cout << res.size() << "\n";
        reverse(res.begin(), res.end());
        for(ll v: res)
        cout << v << ' ';
    }
}

void input()
{
    cin >> n >> m;
    For(i, 1, m)
    {
        ll u, v;
        cin >> u >> v;
        edge[u].push_back(v);
        edge[v].push_back(u);
    }
}

int main()
{
    /* freopen("test.in", "r", stdin);
    freopen("test.ok", "w", stdout); */
    input();
    process();
}