#include <bits/stdc++.h>
using namespace std;

const int N_MAX = 1e5 + 1;
const int M_MAX = 5e5 + 1;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int N, M;
vector<vector<pair<int, int>>> graph(N_MAX, vector<pair<int, int>>());

stack<int> sol;

vector<int> viz(M_MAX, false);

void dfs_euler_cycle(int node)
{
    while(graph[node].size())
    {
        int next = graph[node].back().first;
        int edge_nr = graph[node].back().second;
        graph[node].pop_back();

        if(viz[edge_nr] == false)
        {
            viz[edge_nr] = true;

            dfs_euler_cycle(next);
        }
    }

    sol.push(node);
}

int main()
{
    ios_base::sync_with_stdio(false);
    fin.tie(0);
    fout.tie(0);

    fin >> N >> M;

    for(int i = 1; i <= M; ++i)
    {
        int x, y;
        fin >> x >> y;

        graph[x].push_back({y, i});
        graph[y].push_back({x, i});
    }

    for(int i = 1; i <= N; ++i)
    {
        if(graph[i].size() & 1)
        {
            cout << -1;
            return 0;
        }
    }

    dfs_euler_cycle(1);

    while(sol.size() != 1)
    {
        fout << sol.top() << ' ';
        sol.pop();
    }
}