#include<bits/stdc++.h>

using namespace std;

#define maxn 3010

int n, m;
set<int> adj[maxn];
set<int> g[maxn];
set<int> deleted;
int deg[maxn];
vector<int> tmp;

void dfs(int u)
{
    while (g[u].size())
    {
        int v = *g[u].begin();
        g[u].erase(v);
        g[v].erase(u);
        dfs(v);
    }
    tmp.push_back(u);
}

void check(int root)
{
    int cnt = 0;
    for (int i = 1; i <= n; i++)
        if (deg[i] % 2 == 1) cnt++;
    if (cnt != 0 && cnt != 2) return;
    tmp.clear();
    for (int i = 1; i <= n; i++) g[i] = adj[i];
    dfs(root);

    if (tmp.size() - 1 != m) return;
    for (int i = 1; i <= n; i++) g[i] = adj[i];
    for (int i = 0; i < tmp.size() - 1; i++)
    {
        if (g[tmp[i]].count(tmp[i + 1]) == 0) return;
        g[tmp[i]].erase(tmp[i + 1]);
        g[tmp[i + 1]].erase(tmp[i]);
    }

    if (deleted.size())
    {
        tmp.push_back(-1);
        for (auto v: deleted)
        {
            tmp.push_back(v);
            tmp.push_back(root);
        }
    }

    cout << tmp.size() << endl;
    for (auto x: tmp) cout << x << " ";
    exit(0);
}

void solve(int root)
{
    deleted.clear();
    set<int> droot = adj[root];
    for (auto v: droot)
        if (deg[v] % 2 == 1)
        {
            adj[root].erase(v);
            adj[v].erase(root);
            deg[root]--;
            deg[v]--;
            deleted.insert(v);
            m--;
        }

    check(root);

    droot = adj[root];
    for (auto v: droot)
    {
        adj[root].erase(v);
        adj[v].erase(root);
        deg[root]--;
        deg[v]--;
        deleted.insert(v);
        m--;
        check(root);
        adj[root].insert(v);
        adj[v].insert(root);
        deg[root]++;
        deg[v]++;
        deleted.erase(v);
        m++;
    }

    droot = deleted;
    for (auto v: droot)
    {
        adj[root].insert(v);
        adj[v].insert(root);
        deg[root]++;
        deg[v]++;
        deleted.erase(v);
        m++;
        check(root);
        adj[root].erase(v);
        adj[v].erase(root);
        deg[root]--;
        deg[v]--;
        deleted.insert(v);
        m--;
    }

    for (auto v: deleted)
    {
        adj[root].insert(v);
        adj[v].insert(root);
        deg[root]++;
        deg[v]++;
        m++;
    }
}

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

    cin >> n >> m;
    memset(deg, 0, sizeof(deg));
    for (int i = 1; i <= n; i++) adj[i].clear();
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        cin >> u >> v;
        adj[u].insert(v);
        adj[v].insert(u);
        deg[u]++;
        deg[v]++;
    }

    for (int root = 1; root <= n; root++) solve(root);
    cout << 0;
    return 0;
}
