#include <bits/stdc++.h>

using namespace std;

const int NMAX = 100005;
const int MMAX = 500005;
int N, M;
vector < pair <int, int> > graph[NMAX];
bool usedEdge[MMAX];
int deg[NMAX];
vector <int> answer;

void dfs(int node)
{
    while (!graph[node].empty())
    {
        int nextNode = graph[node].back().first;
        int indEdge = graph[node].back().second;
        graph[node].pop_back();
        if (usedEdge[indEdge] == false)
        {
            usedEdge[indEdge] = true;
            dfs(nextNode);
        }
    }
    answer.push_back(node);
}

int main()
{
    ifstream fin("ciclueuler.in");
    ofstream fout("ciclueuler.out");
    fin >> N >> M;
    for (int i = 1;i <= M;++i)
    {
        int u, v;
        fin >> u >> v;
        graph[u].push_back(make_pair(v, i));
        graph[v].push_back(make_pair(u, i));
        ++deg[u];
        ++deg[v];
    }
    for (int i = 1;i <= N;++i)
        if (deg[i] % 2)
        {
            fout << "-1\n";

            return 0;
        }
    dfs(1);
    answer.pop_back();
    for (auto& i : answer)
        fout << i << " ";
    fin.close();
    fout.close();
    return 0;
}